net: Allow binding of unspecified address without address existance

[dragonfly.git] / crypto / openssh / misc.c

/* $OpenBSD: misc.c,v 1.170 2021/09/26 14:01:03 djm Exp $ */
/*
 * Copyright (c) 2000 Markus Friedl.  All rights reserved.
 * Copyright (c) 2005-2020 Damien Miller.  All rights reserved.
 * Copyright (c) 2004 Henning Brauer <henning@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */


#include "includes.h"

#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/wait.h>
#include <sys/un.h>

#include <limits.h>
#ifdef HAVE_LIBGEN_H
# include <libgen.h>
#endif
#ifdef HAVE_POLL_H
#include <poll.h>
#endif
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>

#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <netdb.h>
#ifdef HAVE_PATHS_H
# include <paths.h>
#include <pwd.h>
#include <grp.h>
#endif
#ifdef SSH_TUN_OPENBSD
#include <net/if.h>
#endif

#include "xmalloc.h"
#include "misc.h"
#include "log.h"
#include "ssh.h"
#include "sshbuf.h"
#include "ssherr.h"
#include "platform.h"

/* remove newline at end of string */
char *
chop(char *s)
{
        char *t = s;
        while (*t) {
                if (*t == '\n' || *t == '\r') {
                        *t = '\0';
                        return s;
                }
                t++;
        }
        return s;

}

/* remove whitespace from end of string */
void
rtrim(char *s)
{
        size_t i;

        if ((i = strlen(s)) == 0)
                return;
        for (i--; i > 0; i--) {
                if (isspace((int)s[i]))
                        s[i] = '\0';
        }
}

/* set/unset filedescriptor to non-blocking */
int
set_nonblock(int fd)
{
        int val;

        val = fcntl(fd, F_GETFL);
        if (val == -1) {
                error("fcntl(%d, F_GETFL): %s", fd, strerror(errno));
                return (-1);
        }
        if (val & O_NONBLOCK) {
                debug3("fd %d is O_NONBLOCK", fd);
                return (0);
        }
        debug2("fd %d setting O_NONBLOCK", fd);
        val |= O_NONBLOCK;
        if (fcntl(fd, F_SETFL, val) == -1) {
                debug("fcntl(%d, F_SETFL, O_NONBLOCK): %s", fd,
                    strerror(errno));
                return (-1);
        }
        return (0);
}

int
unset_nonblock(int fd)
{
        int val;

        val = fcntl(fd, F_GETFL);
        if (val == -1) {
                error("fcntl(%d, F_GETFL): %s", fd, strerror(errno));
                return (-1);
        }
        if (!(val & O_NONBLOCK)) {
                debug3("fd %d is not O_NONBLOCK", fd);
                return (0);
        }
        debug("fd %d clearing O_NONBLOCK", fd);
        val &= ~O_NONBLOCK;
        if (fcntl(fd, F_SETFL, val) == -1) {
                debug("fcntl(%d, F_SETFL, ~O_NONBLOCK): %s",
                    fd, strerror(errno));
                return (-1);
        }
        return (0);
}

const char *
ssh_gai_strerror(int gaierr)
{
        if (gaierr == EAI_SYSTEM && errno != 0)
                return strerror(errno);
        return gai_strerror(gaierr);
}

/* disable nagle on socket */
void
set_nodelay(int fd)
{
        int opt;
        socklen_t optlen;

        optlen = sizeof opt;
        if (getsockopt(fd, IPPROTO_TCP, TCP_NODELAY, &opt, &optlen) == -1) {
                debug("getsockopt TCP_NODELAY: %.100s", strerror(errno));
                return;
        }
        if (opt == 1) {
                debug2("fd %d is TCP_NODELAY", fd);
                return;
        }
        opt = 1;
        debug2("fd %d setting TCP_NODELAY", fd);
        if (setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, &opt, sizeof opt) == -1)
                error("setsockopt TCP_NODELAY: %.100s", strerror(errno));
}

/* Allow local port reuse in TIME_WAIT */
int
set_reuseaddr(int fd)
{
        int on = 1;

        if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) == -1) {
                error("setsockopt SO_REUSEADDR fd %d: %s", fd, strerror(errno));
                return -1;
        }
        return 0;
}

/* Get/set routing domain */
char *
get_rdomain(int fd)
{
#if defined(HAVE_SYS_GET_RDOMAIN)
        return sys_get_rdomain(fd);
#elif defined(__OpenBSD__)
        int rtable;
        char *ret;
        socklen_t len = sizeof(rtable);

        if (getsockopt(fd, SOL_SOCKET, SO_RTABLE, &rtable, &len) == -1) {
                error("Failed to get routing domain for fd %d: %s",
                    fd, strerror(errno));
                return NULL;
        }
        xasprintf(&ret, "%d", rtable);
        return ret;
#else /* defined(__OpenBSD__) */
        return NULL;
#endif
}

int
set_rdomain(int fd, const char *name)
{
#if defined(HAVE_SYS_SET_RDOMAIN)
        return sys_set_rdomain(fd, name);
#elif defined(__OpenBSD__)
        int rtable;
        const char *errstr;

        if (name == NULL)
                return 0; /* default table */

        rtable = (int)strtonum(name, 0, 255, &errstr);
        if (errstr != NULL) {
                /* Shouldn't happen */
                error("Invalid routing domain \"%s\": %s", name, errstr);
                return -1;
        }
        if (setsockopt(fd, SOL_SOCKET, SO_RTABLE,
            &rtable, sizeof(rtable)) == -1) {
                error("Failed to set routing domain %d on fd %d: %s",
                    rtable, fd, strerror(errno));
                return -1;
        }
        return 0;
#else /* defined(__OpenBSD__) */
        error("Setting routing domain is not supported on this platform");
        return -1;
#endif
}

int
get_sock_af(int fd)
{
        struct sockaddr_storage to;
        socklen_t tolen = sizeof(to);

        memset(&to, 0, sizeof(to));
        if (getsockname(fd, (struct sockaddr *)&to, &tolen) == -1)
                return -1;
#ifdef IPV4_IN_IPV6
        if (to.ss_family == AF_INET6 &&
            IN6_IS_ADDR_V4MAPPED(&((struct sockaddr_in6 *)&to)->sin6_addr))
                return AF_INET;
#endif
        return to.ss_family;
}

void
set_sock_tos(int fd, int tos)
{
#ifndef IP_TOS_IS_BROKEN
        int af;

        switch ((af = get_sock_af(fd))) {
        case -1:
                /* assume not a socket */
                break;
        case AF_INET:
# ifdef IP_TOS
                debug3_f("set socket %d IP_TOS 0x%02x", fd, tos);
                if (setsockopt(fd, IPPROTO_IP, IP_TOS,
                    &tos, sizeof(tos)) == -1) {
                        error("setsockopt socket %d IP_TOS %d: %s:",
                            fd, tos, strerror(errno));
                }
# endif /* IP_TOS */
                break;
        case AF_INET6:
# ifdef IPV6_TCLASS
                debug3_f("set socket %d IPV6_TCLASS 0x%02x", fd, tos);
                if (setsockopt(fd, IPPROTO_IPV6, IPV6_TCLASS,
                    &tos, sizeof(tos)) == -1) {
                        error("setsockopt socket %d IPV6_TCLASS %d: %.100s:",
                            fd, tos, strerror(errno));
                }
# endif /* IPV6_TCLASS */
                break;
        default:
                debug2_f("unsupported socket family %d", af);
                break;
        }
#endif /* IP_TOS_IS_BROKEN */
}

/*
 * Wait up to *timeoutp milliseconds for events on fd. Updates
 * *timeoutp with time remaining.
 * Returns 0 if fd ready or -1 on timeout or error (see errno).
 */
static int
waitfd(int fd, int *timeoutp, short events)
{
        struct pollfd pfd;
        struct timeval t_start;
        int oerrno, r;

        pfd.fd = fd;
        pfd.events = events;
        for (; *timeoutp >= 0;) {
                monotime_tv(&t_start);
                r = poll(&pfd, 1, *timeoutp);
                oerrno = errno;
                ms_subtract_diff(&t_start, timeoutp);
                errno = oerrno;
                if (r > 0)
                        return 0;
                else if (r == -1 && errno != EAGAIN && errno != EINTR)
                        return -1;
                else if (r == 0)
                        break;
        }
        /* timeout */
        errno = ETIMEDOUT;
        return -1;
}

/*
 * Wait up to *timeoutp milliseconds for fd to be readable. Updates
 * *timeoutp with time remaining.
 * Returns 0 if fd ready or -1 on timeout or error (see errno).
 */
int
waitrfd(int fd, int *timeoutp) {
        return waitfd(fd, timeoutp, POLLIN);
}

/*
 * Attempt a non-blocking connect(2) to the specified address, waiting up to
 * *timeoutp milliseconds for the connection to complete. If the timeout is
 * <=0, then wait indefinitely.
 *
 * Returns 0 on success or -1 on failure.
 */
int
timeout_connect(int sockfd, const struct sockaddr *serv_addr,
    socklen_t addrlen, int *timeoutp)
{
        int optval = 0;
        socklen_t optlen = sizeof(optval);

        /* No timeout: just do a blocking connect() */
        if (timeoutp == NULL || *timeoutp <= 0)
                return connect(sockfd, serv_addr, addrlen);

        set_nonblock(sockfd);
        for (;;) {
                if (connect(sockfd, serv_addr, addrlen) == 0) {
                        /* Succeeded already? */
                        unset_nonblock(sockfd);
                        return 0;
                } else if (errno == EINTR)
                        continue;
                else if (errno != EINPROGRESS)
                        return -1;
                break;
        }

        if (waitfd(sockfd, timeoutp, POLLIN | POLLOUT) == -1)
                return -1;

        /* Completed or failed */
        if (getsockopt(sockfd, SOL_SOCKET, SO_ERROR, &optval, &optlen) == -1) {
                debug("getsockopt: %s", strerror(errno));
                return -1;
        }
        if (optval != 0) {
                errno = optval;
                return -1;
        }
        unset_nonblock(sockfd);
        return 0;
}

/* Characters considered whitespace in strsep calls. */
#define WHITESPACE " \t\r\n"
#define QUOTE   "\""

/* return next token in configuration line */
static char *
strdelim_internal(char **s, int split_equals)
{
        char *old;
        int wspace = 0;

        if (*s == NULL)
                return NULL;

        old = *s;

        *s = strpbrk(*s,
            split_equals ? WHITESPACE QUOTE "=" : WHITESPACE QUOTE);
        if (*s == NULL)
                return (old);

        if (*s[0] == '\"') {
                memmove(*s, *s + 1, strlen(*s)); /* move nul too */
                /* Find matching quote */
                if ((*s = strpbrk(*s, QUOTE)) == NULL) {
                        return (NULL);          /* no matching quote */
                } else {
                        *s[0] = '\0';
                        *s += strspn(*s + 1, WHITESPACE) + 1;
                        return (old);
                }
        }

        /* Allow only one '=' to be skipped */
        if (split_equals && *s[0] == '=')
                wspace = 1;
        *s[0] = '\0';

        /* Skip any extra whitespace after first token */
        *s += strspn(*s + 1, WHITESPACE) + 1;
        if (split_equals && *s[0] == '=' && !wspace)
                *s += strspn(*s + 1, WHITESPACE) + 1;

        return (old);
}

/*
 * Return next token in configuration line; splts on whitespace or a
 * single '=' character.
 */
char *
strdelim(char **s)
{
        return strdelim_internal(s, 1);
}

/*
 * Return next token in configuration line; splts on whitespace only.
 */
char *
strdelimw(char **s)
{
        return strdelim_internal(s, 0);
}

struct passwd *
pwcopy(struct passwd *pw)
{
        struct passwd *copy = xcalloc(1, sizeof(*copy));

        copy->pw_name = xstrdup(pw->pw_name);
        copy->pw_passwd = xstrdup(pw->pw_passwd == NULL ? "*" : pw->pw_passwd);
#ifdef HAVE_STRUCT_PASSWD_PW_GECOS
        copy->pw_gecos = xstrdup(pw->pw_gecos);
#endif
        copy->pw_uid = pw->pw_uid;
        copy->pw_gid = pw->pw_gid;
#ifdef HAVE_STRUCT_PASSWD_PW_EXPIRE
        copy->pw_expire = pw->pw_expire;
#endif
#ifdef HAVE_STRUCT_PASSWD_PW_CHANGE
        copy->pw_change = pw->pw_change;
#endif
#ifdef HAVE_STRUCT_PASSWD_PW_CLASS
        copy->pw_class = xstrdup(pw->pw_class);
#endif
        copy->pw_dir = xstrdup(pw->pw_dir);
        copy->pw_shell = xstrdup(pw->pw_shell);
        return copy;
}

/*
 * Convert ASCII string to TCP/IP port number.
 * Port must be >=0 and <=65535.
 * Return -1 if invalid.
 */
int
a2port(const char *s)
{
        struct servent *se;
        long long port;
        const char *errstr;

        port = strtonum(s, 0, 65535, &errstr);
        if (errstr == NULL)
                return (int)port;
        if ((se = getservbyname(s, "tcp")) != NULL)
                return ntohs(se->s_port);
        return -1;
}

int
a2tun(const char *s, int *remote)
{
        const char *errstr = NULL;
        char *sp, *ep;
        int tun;

        if (remote != NULL) {
                *remote = SSH_TUNID_ANY;
                sp = xstrdup(s);
                if ((ep = strchr(sp, ':')) == NULL) {
                        free(sp);
                        return (a2tun(s, NULL));
                }
                ep[0] = '\0'; ep++;
                *remote = a2tun(ep, NULL);
                tun = a2tun(sp, NULL);
                free(sp);
                return (*remote == SSH_TUNID_ERR ? *remote : tun);
        }

        if (strcasecmp(s, "any") == 0)
                return (SSH_TUNID_ANY);

        tun = strtonum(s, 0, SSH_TUNID_MAX, &errstr);
        if (errstr != NULL)
                return (SSH_TUNID_ERR);

        return (tun);
}

#define SECONDS         1
#define MINUTES         (SECONDS * 60)
#define HOURS           (MINUTES * 60)
#define DAYS            (HOURS * 24)
#define WEEKS           (DAYS * 7)

/*
 * Convert a time string into seconds; format is
 * a sequence of:
 *      time[qualifier]
 *
 * Valid time qualifiers are:
 *      <none>  seconds
 *      s|S     seconds
 *      m|M     minutes
 *      h|H     hours
 *      d|D     days
 *      w|W     weeks
 *
 * Examples:
 *      90m     90 minutes
 *      1h30m   90 minutes
 *      2d      2 days
 *      1w      1 week
 *
 * Return -1 if time string is invalid.
 */
int
convtime(const char *s)
{
        long total, secs, multiplier;
        const char *p;
        char *endp;

        errno = 0;
        total = 0;
        p = s;

        if (p == NULL || *p == '\0')
                return -1;

        while (*p) {
                secs = strtol(p, &endp, 10);
                if (p == endp ||
                    (errno == ERANGE && (secs == INT_MIN || secs == INT_MAX)) ||
                    secs < 0)
                        return -1;

                multiplier = 1;
                switch (*endp++) {
                case '\0':
                        endp--;
                        break;
                case 's':
                case 'S':
                        break;
                case 'm':
                case 'M':
                        multiplier = MINUTES;
                        break;
                case 'h':
                case 'H':
                        multiplier = HOURS;
                        break;
                case 'd':
                case 'D':
                        multiplier = DAYS;
                        break;
                case 'w':
                case 'W':
                        multiplier = WEEKS;
                        break;
                default:
                        return -1;
                }
                if (secs > INT_MAX / multiplier)
                        return -1;
                secs *= multiplier;
                if  (total > INT_MAX - secs)
                        return -1;
                total += secs;
                if (total < 0)
                        return -1;
                p = endp;
        }

        return total;
}

#define TF_BUFS 8
#define TF_LEN  9

const char *
fmt_timeframe(time_t t)
{
        char            *buf;
        static char      tfbuf[TF_BUFS][TF_LEN];        /* ring buffer */
        static int       idx = 0;
        unsigned int     sec, min, hrs, day;
        unsigned long long      week;

        buf = tfbuf[idx++];
        if (idx == TF_BUFS)
                idx = 0;

        week = t;

        sec = week % 60;
        week /= 60;
        min = week % 60;
        week /= 60;
        hrs = week % 24;
        week /= 24;
        day = week % 7;
        week /= 7;

        if (week > 0)
                snprintf(buf, TF_LEN, "%02lluw%01ud%02uh", week, day, hrs);
        else if (day > 0)
                snprintf(buf, TF_LEN, "%01ud%02uh%02um", day, hrs, min);
        else
                snprintf(buf, TF_LEN, "%02u:%02u:%02u", hrs, min, sec);

        return (buf);
}

/*
 * Returns a standardized host+port identifier string.
 * Caller must free returned string.
 */
char *
put_host_port(const char *host, u_short port)
{
        char *hoststr;

        if (port == 0 || port == SSH_DEFAULT_PORT)
                return(xstrdup(host));
        if (asprintf(&hoststr, "[%s]:%d", host, (int)port) == -1)
                fatal("put_host_port: asprintf: %s", strerror(errno));
        debug3("put_host_port: %s", hoststr);
        return hoststr;
}

/*
 * Search for next delimiter between hostnames/addresses and ports.
 * Argument may be modified (for termination).
 * Returns *cp if parsing succeeds.
 * *cp is set to the start of the next field, if one was found.
 * The delimiter char, if present, is stored in delim.
 * If this is the last field, *cp is set to NULL.
 */
char *
hpdelim2(char **cp, char *delim)
{
        char *s, *old;

        if (cp == NULL || *cp == NULL)
                return NULL;

        old = s = *cp;
        if (*s == '[') {
                if ((s = strchr(s, ']')) == NULL)
                        return NULL;
                else
                        s++;
        } else if ((s = strpbrk(s, ":/")) == NULL)
                s = *cp + strlen(*cp); /* skip to end (see first case below) */

        switch (*s) {
        case '\0':
                *cp = NULL;     /* no more fields*/
                break;

        case ':':
        case '/':
                if (delim != NULL)
                        *delim = *s;
                *s = '\0';      /* terminate */
                *cp = s + 1;
                break;

        default:
                return NULL;
        }

        return old;
}

char *
hpdelim(char **cp)
{
        return hpdelim2(cp, NULL);
}

char *
cleanhostname(char *host)
{
        if (*host == '[' && host[strlen(host) - 1] == ']') {
                host[strlen(host) - 1] = '\0';
                return (host + 1);
        } else
                return host;
}

char *
colon(char *cp)
{
        int flag = 0;

        if (*cp == ':')         /* Leading colon is part of file name. */
                return NULL;
        if (*cp == '[')
                flag = 1;

        for (; *cp; ++cp) {
                if (*cp == '@' && *(cp+1) == '[')
                        flag = 1;
                if (*cp == ']' && *(cp+1) == ':' && flag)
                        return (cp+1);
                if (*cp == ':' && !flag)
                        return (cp);
                if (*cp == '/')
                        return NULL;
        }
        return NULL;
}

/*
 * Parse a [user@]host:[path] string.
 * Caller must free returned user, host and path.
 * Any of the pointer return arguments may be NULL (useful for syntax checking).
 * If user was not specified then *userp will be set to NULL.
 * If host was not specified then *hostp will be set to NULL.
 * If path was not specified then *pathp will be set to ".".
 * Returns 0 on success, -1 on failure.
 */
int
parse_user_host_path(const char *s, char **userp, char **hostp, char **pathp)
{
        char *user = NULL, *host = NULL, *path = NULL;
        char *sdup, *tmp;
        int ret = -1;

        if (userp != NULL)
                *userp = NULL;
        if (hostp != NULL)
                *hostp = NULL;
        if (pathp != NULL)
                *pathp = NULL;

        sdup = xstrdup(s);

        /* Check for remote syntax: [user@]host:[path] */
        if ((tmp = colon(sdup)) == NULL)
                goto out;

        /* Extract optional path */
        *tmp++ = '\0';
        if (*tmp == '\0')
                tmp = ".";
        path = xstrdup(tmp);

        /* Extract optional user and mandatory host */
        tmp = strrchr(sdup, '@');
        if (tmp != NULL) {
                *tmp++ = '\0';
                host = xstrdup(cleanhostname(tmp));
                if (*sdup != '\0')
                        user = xstrdup(sdup);
        } else {
                host = xstrdup(cleanhostname(sdup));
                user = NULL;
        }

        /* Success */
        if (userp != NULL) {
                *userp = user;
                user = NULL;
        }
        if (hostp != NULL) {
                *hostp = host;
                host = NULL;
        }
        if (pathp != NULL) {
                *pathp = path;
                path = NULL;
        }
        ret = 0;
out:
        free(sdup);
        free(user);
        free(host);
        free(path);
        return ret;
}

/*
 * Parse a [user@]host[:port] string.
 * Caller must free returned user and host.
 * Any of the pointer return arguments may be NULL (useful for syntax checking).
 * If user was not specified then *userp will be set to NULL.
 * If port was not specified then *portp will be -1.
 * Returns 0 on success, -1 on failure.
 */
int
parse_user_host_port(const char *s, char **userp, char **hostp, int *portp)
{
        char *sdup, *cp, *tmp;
        char *user = NULL, *host = NULL;
        int port = -1, ret = -1;

        if (userp != NULL)
                *userp = NULL;
        if (hostp != NULL)
                *hostp = NULL;
        if (portp != NULL)
                *portp = -1;

        if ((sdup = tmp = strdup(s)) == NULL)
                return -1;
        /* Extract optional username */
        if ((cp = strrchr(tmp, '@')) != NULL) {
                *cp = '\0';
                if (*tmp == '\0')
                        goto out;
                if ((user = strdup(tmp)) == NULL)
                        goto out;
                tmp = cp + 1;
        }
        /* Extract mandatory hostname */
        if ((cp = hpdelim(&tmp)) == NULL || *cp == '\0')
                goto out;
        host = xstrdup(cleanhostname(cp));
        /* Convert and verify optional port */
        if (tmp != NULL && *tmp != '\0') {
                if ((port = a2port(tmp)) <= 0)
                        goto out;
        }
        /* Success */
        if (userp != NULL) {
                *userp = user;
                user = NULL;
        }
        if (hostp != NULL) {
                *hostp = host;
                host = NULL;
        }
        if (portp != NULL)
                *portp = port;
        ret = 0;
 out:
        free(sdup);
        free(user);
        free(host);
        return ret;
}

/*
 * Converts a two-byte hex string to decimal.
 * Returns the decimal value or -1 for invalid input.
 */
static int
hexchar(const char *s)
{
        unsigned char result[2];
        int i;

        for (i = 0; i < 2; i++) {
                if (s[i] >= '0' && s[i] <= '9')
                        result[i] = (unsigned char)(s[i] - '0');
                else if (s[i] >= 'a' && s[i] <= 'f')
                        result[i] = (unsigned char)(s[i] - 'a') + 10;
                else if (s[i] >= 'A' && s[i] <= 'F')
                        result[i] = (unsigned char)(s[i] - 'A') + 10;
                else
                        return -1;
        }
        return (result[0] << 4) | result[1];
}

/*
 * Decode an url-encoded string.
 * Returns a newly allocated string on success or NULL on failure.
 */
static char *
urldecode(const char *src)
{
        char *ret, *dst;
        int ch;

        ret = xmalloc(strlen(src) + 1);
        for (dst = ret; *src != '\0'; src++) {
                switch (*src) {
                case '+':
                        *dst++ = ' ';
                        break;
                case '%':
                        if (!isxdigit((unsigned char)src[1]) ||
                            !isxdigit((unsigned char)src[2]) ||
                            (ch = hexchar(src + 1)) == -1) {
                                free(ret);
                                return NULL;
                        }
                        *dst++ = ch;
                        src += 2;
                        break;
                default:
                        *dst++ = *src;
                        break;
                }
        }
        *dst = '\0';

        return ret;
}

/*
 * Parse an (scp|ssh|sftp)://[user@]host[:port][/path] URI.
 * See https://tools.ietf.org/html/draft-ietf-secsh-scp-sftp-ssh-uri-04
 * Either user or path may be url-encoded (but not host or port).
 * Caller must free returned user, host and path.
 * Any of the pointer return arguments may be NULL (useful for syntax checking)
 * but the scheme must always be specified.
 * If user was not specified then *userp will be set to NULL.
 * If port was not specified then *portp will be -1.
 * If path was not specified then *pathp will be set to NULL.
 * Returns 0 on success, 1 if non-uri/wrong scheme, -1 on error/invalid uri.
 */
int
parse_uri(const char *scheme, const char *uri, char **userp, char **hostp,
    int *portp, char **pathp)
{
        char *uridup, *cp, *tmp, ch;
        char *user = NULL, *host = NULL, *path = NULL;
        int port = -1, ret = -1;
        size_t len;

        len = strlen(scheme);
        if (strncmp(uri, scheme, len) != 0 || strncmp(uri + len, "://", 3) != 0)
                return 1;
        uri += len + 3;

        if (userp != NULL)
                *userp = NULL;
        if (hostp != NULL)
                *hostp = NULL;
        if (portp != NULL)
                *portp = -1;
        if (pathp != NULL)
                *pathp = NULL;

        uridup = tmp = xstrdup(uri);

        /* Extract optional ssh-info (username + connection params) */
        if ((cp = strchr(tmp, '@')) != NULL) {
                char *delim;

                *cp = '\0';
                /* Extract username and connection params */
                if ((delim = strchr(tmp, ';')) != NULL) {
                        /* Just ignore connection params for now */
                        *delim = '\0';
                }
                if (*tmp == '\0') {
                        /* Empty username */
                        goto out;
                }
                if ((user = urldecode(tmp)) == NULL)
                        goto out;
                tmp = cp + 1;
        }

        /* Extract mandatory hostname */
        if ((cp = hpdelim2(&tmp, &ch)) == NULL || *cp == '\0')
                goto out;
        host = xstrdup(cleanhostname(cp));
        if (!valid_domain(host, 0, NULL))
                goto out;

        if (tmp != NULL && *tmp != '\0') {
                if (ch == ':') {
                        /* Convert and verify port. */
                        if ((cp = strchr(tmp, '/')) != NULL)
                                *cp = '\0';
                        if ((port = a2port(tmp)) <= 0)
                                goto out;
                        tmp = cp ? cp + 1 : NULL;
                }
                if (tmp != NULL && *tmp != '\0') {
                        /* Extract optional path */
                        if ((path = urldecode(tmp)) == NULL)
                                goto out;
                }
        }

        /* Success */
        if (userp != NULL) {
                *userp = user;
                user = NULL;
        }
        if (hostp != NULL) {
                *hostp = host;
                host = NULL;
        }
        if (portp != NULL)
                *portp = port;
        if (pathp != NULL) {
                *pathp = path;
                path = NULL;
        }
        ret = 0;
 out:
        free(uridup);
        free(user);
        free(host);
        free(path);
        return ret;
}

/* function to assist building execv() arguments */
void
addargs(arglist *args, char *fmt, ...)
{
        va_list ap;
        char *cp;
        u_int nalloc;
        int r;

        va_start(ap, fmt);
        r = vasprintf(&cp, fmt, ap);
        va_end(ap);
        if (r == -1)
                fatal("addargs: argument too long");

        nalloc = args->nalloc;
        if (args->list == NULL) {
                nalloc = 32;
                args->num = 0;
        } else if (args->num+2 >= nalloc)
                nalloc *= 2;

        args->list = xrecallocarray(args->list, args->nalloc, nalloc, sizeof(char *));
        args->nalloc = nalloc;
        args->list[args->num++] = cp;
        args->list[args->num] = NULL;
}

void
replacearg(arglist *args, u_int which, char *fmt, ...)
{
        va_list ap;
        char *cp;
        int r;

        va_start(ap, fmt);
        r = vasprintf(&cp, fmt, ap);
        va_end(ap);
        if (r == -1)
                fatal("replacearg: argument too long");

        if (which >= args->num)
                fatal("replacearg: tried to replace invalid arg %d >= %d",
                    which, args->num);
        free(args->list[which]);
        args->list[which] = cp;
}

void
freeargs(arglist *args)
{
        u_int i;

        if (args->list != NULL) {
                for (i = 0; i < args->num; i++)
                        free(args->list[i]);
                free(args->list);
                args->nalloc = args->num = 0;
                args->list = NULL;
        }
}

/*
 * Expands tildes in the file name.  Returns data allocated by xmalloc.
 * Warning: this calls getpw*.
 */
int
tilde_expand(const char *filename, uid_t uid, char **retp)
{
        const char *path, *sep;
        char user[128], *ret;
        struct passwd *pw;
        u_int len, slash;

        if (*filename != '~') {
                *retp = xstrdup(filename);
                return 0;
        }
        filename++;

        path = strchr(filename, '/');
        if (path != NULL && path > filename) {          /* ~user/path */
                slash = path - filename;
                if (slash > sizeof(user) - 1) {
                        error_f("~username too long");
                        return -1;
                }
                memcpy(user, filename, slash);
                user[slash] = '\0';
                if ((pw = getpwnam(user)) == NULL) {
                        error_f("No such user %s", user);
                        return -1;
                }
        } else if ((pw = getpwuid(uid)) == NULL) {      /* ~/path */
                error_f("No such uid %ld", (long)uid);
                return -1;
        }

        /* Make sure directory has a trailing '/' */
        len = strlen(pw->pw_dir);
        if (len == 0 || pw->pw_dir[len - 1] != '/')
                sep = "/";
        else
                sep = "";

        /* Skip leading '/' from specified path */
        if (path != NULL)
                filename = path + 1;

        if (xasprintf(&ret, "%s%s%s", pw->pw_dir, sep, filename) >= PATH_MAX) {
                error_f("Path too long");
                return -1;
        }

        *retp = ret;
        return 0;
}

char *
tilde_expand_filename(const char *filename, uid_t uid)
{
        char *ret;

        if (tilde_expand(filename, uid, &ret) != 0)
                cleanup_exit(255);
        return ret;
}

/*
 * Expand a string with a set of %[char] escapes and/or ${ENVIRONMENT}
 * substitutions.  A number of escapes may be specified as
 * (char *escape_chars, char *replacement) pairs. The list must be terminated
 * by a NULL escape_char. Returns replaced string in memory allocated by
 * xmalloc which the caller must free.
 */
static char *
vdollar_percent_expand(int *parseerror, int dollar, int percent,
    const char *string, va_list ap)
{
#define EXPAND_MAX_KEYS 16
        u_int num_keys = 0, i;
        struct {
                const char *key;
                const char *repl;
        } keys[EXPAND_MAX_KEYS];
        struct sshbuf *buf;
        int r, missingvar = 0;
        char *ret = NULL, *var, *varend, *val;
        size_t len;

        if ((buf = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");
        if (parseerror == NULL)
                fatal_f("null parseerror arg");
        *parseerror = 1;

        /* Gather keys if we're doing percent expansion. */
        if (percent) {
                for (num_keys = 0; num_keys < EXPAND_MAX_KEYS; num_keys++) {
                        keys[num_keys].key = va_arg(ap, char *);
                        if (keys[num_keys].key == NULL)
                                break;
                        keys[num_keys].repl = va_arg(ap, char *);
                        if (keys[num_keys].repl == NULL) {
                                fatal_f("NULL replacement for token %s",
                                    keys[num_keys].key);
                        }
                }
                if (num_keys == EXPAND_MAX_KEYS && va_arg(ap, char *) != NULL)
                        fatal_f("too many keys");
                if (num_keys == 0)
                        fatal_f("percent expansion without token list");
        }

        /* Expand string */
        for (i = 0; *string != '\0'; string++) {
                /* Optionally process ${ENVIRONMENT} expansions. */
                if (dollar && string[0] == '$' && string[1] == '{') {
                        string += 2;  /* skip over '${' */
                        if ((varend = strchr(string, '}')) == NULL) {
                                error_f("environment variable '%s' missing "
                                    "closing '}'", string);
                                goto out;
                        }
                        len = varend - string;
                        if (len == 0) {
                                error_f("zero-length environment variable");
                                goto out;
                        }
                        var = xmalloc(len + 1);
                        (void)strlcpy(var, string, len + 1);
                        if ((val = getenv(var)) == NULL) {
                                error_f("env var ${%s} has no value", var);
                                missingvar = 1;
                        } else {
                                debug3_f("expand ${%s} -> '%s'", var, val);
                                if ((r = sshbuf_put(buf, val, strlen(val))) !=0)
                                        fatal_fr(r, "sshbuf_put ${}");
                        }
                        free(var);
                        string += len;
                        continue;
                }

                /*
                 * Process percent expansions if we have a list of TOKENs.
                 * If we're not doing percent expansion everything just gets
                 * appended here.
                 */
                if (*string != '%' || !percent) {
 append:
                        if ((r = sshbuf_put_u8(buf, *string)) != 0)
                                fatal_fr(r, "sshbuf_put_u8 %%");
                        continue;
                }
                string++;
                /* %% case */
                if (*string == '%')
                        goto append;
                if (*string == '\0') {
                        error_f("invalid format");
                        goto out;
                }
                for (i = 0; i < num_keys; i++) {
                        if (strchr(keys[i].key, *string) != NULL) {
                                if ((r = sshbuf_put(buf, keys[i].repl,
                                    strlen(keys[i].repl))) != 0)
                                        fatal_fr(r, "sshbuf_put %%-repl");
                                break;
                        }
                }
                if (i >= num_keys) {
                        error_f("unknown key %%%c", *string);
                        goto out;
                }
        }
        if (!missingvar && (ret = sshbuf_dup_string(buf)) == NULL)
                fatal_f("sshbuf_dup_string failed");
        *parseerror = 0;
 out:
        sshbuf_free(buf);
        return *parseerror ? NULL : ret;
#undef EXPAND_MAX_KEYS
}

/*
 * Expand only environment variables.
 * Note that although this function is variadic like the other similar
 * functions, any such arguments will be unused.
 */

char *
dollar_expand(int *parseerr, const char *string, ...)
{
        char *ret;
        int err;
        va_list ap;

        va_start(ap, string);
        ret = vdollar_percent_expand(&err, 1, 0, string, ap);
        va_end(ap);
        if (parseerr != NULL)
                *parseerr = err;
        return ret;
}

/*
 * Returns expanded string or NULL if a specified environment variable is
 * not defined, or calls fatal if the string is invalid.
 */
char *
percent_expand(const char *string, ...)
{
        char *ret;
        int err;
        va_list ap;

        va_start(ap, string);
        ret = vdollar_percent_expand(&err, 0, 1, string, ap);
        va_end(ap);
        if (err)
                fatal_f("failed");
        return ret;
}

/*
 * Returns expanded string or NULL if a specified environment variable is
 * not defined, or calls fatal if the string is invalid.
 */
char *
percent_dollar_expand(const char *string, ...)
{
        char *ret;
        int err;
        va_list ap;

        va_start(ap, string);
        ret = vdollar_percent_expand(&err, 1, 1, string, ap);
        va_end(ap);
        if (err)
                fatal_f("failed");
        return ret;
}

int
tun_open(int tun, int mode, char **ifname)
{
#if defined(CUSTOM_SYS_TUN_OPEN)
        return (sys_tun_open(tun, mode, ifname));
#elif defined(SSH_TUN_OPENBSD)
        struct ifreq ifr;
        char name[100];
        int fd = -1, sock;
        const char *tunbase = "tun";

        if (ifname != NULL)
                *ifname = NULL;

        if (mode == SSH_TUNMODE_ETHERNET)
                tunbase = "tap";

        /* Open the tunnel device */
        if (tun <= SSH_TUNID_MAX) {
                snprintf(name, sizeof(name), "/dev/%s%d", tunbase, tun);
                fd = open(name, O_RDWR);
        } else if (tun == SSH_TUNID_ANY) {
                for (tun = 100; tun >= 0; tun--) {
                        snprintf(name, sizeof(name), "/dev/%s%d",
                            tunbase, tun);
                        if ((fd = open(name, O_RDWR)) >= 0)
                                break;
                }
        } else {
                debug_f("invalid tunnel %u", tun);
                return -1;
        }

        if (fd == -1) {
                debug_f("%s open: %s", name, strerror(errno));
                return -1;
        }

        debug_f("%s mode %d fd %d", name, mode, fd);

        /* Bring interface up if it is not already */
        snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "%s%d", tunbase, tun);
        if ((sock = socket(PF_UNIX, SOCK_STREAM, 0)) == -1)
                goto failed;

        if (ioctl(sock, SIOCGIFFLAGS, &ifr) == -1) {
                debug_f("get interface %s flags: %s", ifr.ifr_name,
                    strerror(errno));
                goto failed;
        }

        if (!(ifr.ifr_flags & IFF_UP)) {
                ifr.ifr_flags |= IFF_UP;
                if (ioctl(sock, SIOCSIFFLAGS, &ifr) == -1) {
                        debug_f("activate interface %s: %s", ifr.ifr_name,
                            strerror(errno));
                        goto failed;
                }
        }

        if (ifname != NULL)
                *ifname = xstrdup(ifr.ifr_name);

        close(sock);
        return fd;

 failed:
        if (fd >= 0)
                close(fd);
        if (sock >= 0)
                close(sock);
        return -1;
#else
        error("Tunnel interfaces are not supported on this platform");
        return (-1);
#endif
}

void
sanitise_stdfd(void)
{
        int nullfd, dupfd;

        if ((nullfd = dupfd = open(_PATH_DEVNULL, O_RDWR)) == -1) {
                fprintf(stderr, "Couldn't open /dev/null: %s\n",
                    strerror(errno));
                exit(1);
        }
        while (++dupfd <= STDERR_FILENO) {
                /* Only populate closed fds. */
                if (fcntl(dupfd, F_GETFL) == -1 && errno == EBADF) {
                        if (dup2(nullfd, dupfd) == -1) {
                                fprintf(stderr, "dup2: %s\n", strerror(errno));
                                exit(1);
                        }
                }
        }
        if (nullfd > STDERR_FILENO)
                close(nullfd);
}

char *
tohex(const void *vp, size_t l)
{
        const u_char *p = (const u_char *)vp;
        char b[3], *r;
        size_t i, hl;

        if (l > 65536)
                return xstrdup("tohex: length > 65536");

        hl = l * 2 + 1;
        r = xcalloc(1, hl);
        for (i = 0; i < l; i++) {
                snprintf(b, sizeof(b), "%02x", p[i]);
                strlcat(r, b, hl);
        }
        return (r);
}

/*
 * Extend string *sp by the specified format. If *sp is not NULL (or empty),
 * then the separator 'sep' will be prepended before the formatted arguments.
 * Extended strings are heap allocated.
 */
void
xextendf(char **sp, const char *sep, const char *fmt, ...)
{
        va_list ap;
        char *tmp1, *tmp2;

        va_start(ap, fmt);
        xvasprintf(&tmp1, fmt, ap);
        va_end(ap);

        if (*sp == NULL || **sp == '\0') {
                free(*sp);
                *sp = tmp1;
                return;
        }
        xasprintf(&tmp2, "%s%s%s", *sp, sep == NULL ? "" : sep, tmp1);
        free(tmp1);
        free(*sp);
        *sp = tmp2;
}


u_int64_t
get_u64(const void *vp)
{
        const u_char *p = (const u_char *)vp;
        u_int64_t v;

        v  = (u_int64_t)p[0] << 56;
        v |= (u_int64_t)p[1] << 48;
        v |= (u_int64_t)p[2] << 40;
        v |= (u_int64_t)p[3] << 32;
        v |= (u_int64_t)p[4] << 24;
        v |= (u_int64_t)p[5] << 16;
        v |= (u_int64_t)p[6] << 8;
        v |= (u_int64_t)p[7];

        return (v);
}

u_int32_t
get_u32(const void *vp)
{
        const u_char *p = (const u_char *)vp;
        u_int32_t v;

        v  = (u_int32_t)p[0] << 24;
        v |= (u_int32_t)p[1] << 16;
        v |= (u_int32_t)p[2] << 8;
        v |= (u_int32_t)p[3];

        return (v);
}

u_int32_t
get_u32_le(const void *vp)
{
        const u_char *p = (const u_char *)vp;
        u_int32_t v;

        v  = (u_int32_t)p[0];
        v |= (u_int32_t)p[1] << 8;
        v |= (u_int32_t)p[2] << 16;
        v |= (u_int32_t)p[3] << 24;

        return (v);
}

u_int16_t
get_u16(const void *vp)
{
        const u_char *p = (const u_char *)vp;
        u_int16_t v;

        v  = (u_int16_t)p[0] << 8;
        v |= (u_int16_t)p[1];

        return (v);
}

void
put_u64(void *vp, u_int64_t v)
{
        u_char *p = (u_char *)vp;

        p[0] = (u_char)(v >> 56) & 0xff;
        p[1] = (u_char)(v >> 48) & 0xff;
        p[2] = (u_char)(v >> 40) & 0xff;
        p[3] = (u_char)(v >> 32) & 0xff;
        p[4] = (u_char)(v >> 24) & 0xff;
        p[5] = (u_char)(v >> 16) & 0xff;
        p[6] = (u_char)(v >> 8) & 0xff;
        p[7] = (u_char)v & 0xff;
}

void
put_u32(void *vp, u_int32_t v)
{
        u_char *p = (u_char *)vp;

        p[0] = (u_char)(v >> 24) & 0xff;
        p[1] = (u_char)(v >> 16) & 0xff;
        p[2] = (u_char)(v >> 8) & 0xff;
        p[3] = (u_char)v & 0xff;
}

void
put_u32_le(void *vp, u_int32_t v)
{
        u_char *p = (u_char *)vp;

        p[0] = (u_char)v & 0xff;
        p[1] = (u_char)(v >> 8) & 0xff;
        p[2] = (u_char)(v >> 16) & 0xff;
        p[3] = (u_char)(v >> 24) & 0xff;
}

void
put_u16(void *vp, u_int16_t v)
{
        u_char *p = (u_char *)vp;

        p[0] = (u_char)(v >> 8) & 0xff;
        p[1] = (u_char)v & 0xff;
}

void
ms_subtract_diff(struct timeval *start, int *ms)
{
        struct timeval diff, finish;

        monotime_tv(&finish);
        timersub(&finish, start, &diff);
        *ms -= (diff.tv_sec * 1000) + (diff.tv_usec / 1000);
}

void
ms_to_timeval(struct timeval *tv, int ms)
{
        if (ms < 0)
                ms = 0;
        tv->tv_sec = ms / 1000;
        tv->tv_usec = (ms % 1000) * 1000;
}

void
monotime_ts(struct timespec *ts)
{
        struct timeval tv;
#if defined(HAVE_CLOCK_GETTIME) && (defined(CLOCK_BOOTTIME) || \
    defined(CLOCK_MONOTONIC) || defined(CLOCK_REALTIME))
        static int gettime_failed = 0;

        if (!gettime_failed) {
# ifdef CLOCK_BOOTTIME
                if (clock_gettime(CLOCK_BOOTTIME, ts) == 0)
                        return;
# endif /* CLOCK_BOOTTIME */
# ifdef CLOCK_MONOTONIC
                if (clock_gettime(CLOCK_MONOTONIC, ts) == 0)
                        return;
# endif /* CLOCK_MONOTONIC */
# ifdef CLOCK_REALTIME
                /* Not monotonic, but we're almost out of options here. */
                if (clock_gettime(CLOCK_REALTIME, ts) == 0)
                        return;
# endif /* CLOCK_REALTIME */
                debug3("clock_gettime: %s", strerror(errno));
                gettime_failed = 1;
        }
#endif /* HAVE_CLOCK_GETTIME && (BOOTTIME || MONOTONIC || REALTIME) */
        gettimeofday(&tv, NULL);
        ts->tv_sec = tv.tv_sec;
        ts->tv_nsec = (long)tv.tv_usec * 1000;
}

void
monotime_tv(struct timeval *tv)
{
        struct timespec ts;

        monotime_ts(&ts);
        tv->tv_sec = ts.tv_sec;
        tv->tv_usec = ts.tv_nsec / 1000;
}

time_t
monotime(void)
{
        struct timespec ts;

        monotime_ts(&ts);
        return ts.tv_sec;
}

double
monotime_double(void)
{
        struct timespec ts;

        monotime_ts(&ts);
        return ts.tv_sec + ((double)ts.tv_nsec / 1000000000);
}

void
bandwidth_limit_init(struct bwlimit *bw, u_int64_t kbps, size_t buflen)
{
        bw->buflen = buflen;
        bw->rate = kbps;
        bw->thresh = buflen;
        bw->lamt = 0;
        timerclear(&bw->bwstart);
        timerclear(&bw->bwend);
}

/* Callback from read/write loop to insert bandwidth-limiting delays */
void
bandwidth_limit(struct bwlimit *bw, size_t read_len)
{
        u_int64_t waitlen;
        struct timespec ts, rm;

        bw->lamt += read_len;
        if (!timerisset(&bw->bwstart)) {
                monotime_tv(&bw->bwstart);
                return;
        }
        if (bw->lamt < bw->thresh)
                return;

        monotime_tv(&bw->bwend);
        timersub(&bw->bwend, &bw->bwstart, &bw->bwend);
        if (!timerisset(&bw->bwend))
                return;

        bw->lamt *= 8;
        waitlen = (double)1000000L * bw->lamt / bw->rate;

        bw->bwstart.tv_sec = waitlen / 1000000L;
        bw->bwstart.tv_usec = waitlen % 1000000L;

        if (timercmp(&bw->bwstart, &bw->bwend, >)) {
                timersub(&bw->bwstart, &bw->bwend, &bw->bwend);

                /* Adjust the wait time */
                if (bw->bwend.tv_sec) {
                        bw->thresh /= 2;
                        if (bw->thresh < bw->buflen / 4)
                                bw->thresh = bw->buflen / 4;
                } else if (bw->bwend.tv_usec < 10000) {
                        bw->thresh *= 2;
                        if (bw->thresh > bw->buflen * 8)
                                bw->thresh = bw->buflen * 8;
                }

                TIMEVAL_TO_TIMESPEC(&bw->bwend, &ts);
                while (nanosleep(&ts, &rm) == -1) {
                        if (errno != EINTR)
                                break;
                        ts = rm;
                }
        }

        bw->lamt = 0;
        monotime_tv(&bw->bwstart);
}

/* Make a template filename for mk[sd]temp() */
void
mktemp_proto(char *s, size_t len)
{
        const char *tmpdir;
        int r;

        if ((tmpdir = getenv("TMPDIR")) != NULL) {
                r = snprintf(s, len, "%s/ssh-XXXXXXXXXXXX", tmpdir);
                if (r > 0 && (size_t)r < len)
                        return;
        }
        r = snprintf(s, len, "/tmp/ssh-XXXXXXXXXXXX");
        if (r < 0 || (size_t)r >= len)
                fatal_f("template string too short");
}

static const struct {
        const char *name;
        int value;
} ipqos[] = {
        { "none", INT_MAX },            /* can't use 0 here; that's CS0 */
        { "af11", IPTOS_DSCP_AF11 },
        { "af12", IPTOS_DSCP_AF12 },
        { "af13", IPTOS_DSCP_AF13 },
        { "af21", IPTOS_DSCP_AF21 },
        { "af22", IPTOS_DSCP_AF22 },
        { "af23", IPTOS_DSCP_AF23 },
        { "af31", IPTOS_DSCP_AF31 },
        { "af32", IPTOS_DSCP_AF32 },
        { "af33", IPTOS_DSCP_AF33 },
        { "af41", IPTOS_DSCP_AF41 },
        { "af42", IPTOS_DSCP_AF42 },
        { "af43", IPTOS_DSCP_AF43 },
        { "cs0", IPTOS_DSCP_CS0 },
        { "cs1", IPTOS_DSCP_CS1 },
        { "cs2", IPTOS_DSCP_CS2 },
        { "cs3", IPTOS_DSCP_CS3 },
        { "cs4", IPTOS_DSCP_CS4 },
        { "cs5", IPTOS_DSCP_CS5 },
        { "cs6", IPTOS_DSCP_CS6 },
        { "cs7", IPTOS_DSCP_CS7 },
        { "ef", IPTOS_DSCP_EF },
        { "le", IPTOS_DSCP_LE },
        { "lowdelay", IPTOS_LOWDELAY },
        { "throughput", IPTOS_THROUGHPUT },
        { "reliability", IPTOS_RELIABILITY },
        { NULL, -1 }
};

int
parse_ipqos(const char *cp)
{
        u_int i;
        char *ep;
        long val;

        if (cp == NULL)
                return -1;
        for (i = 0; ipqos[i].name != NULL; i++) {
                if (strcasecmp(cp, ipqos[i].name) == 0)
                        return ipqos[i].value;
        }
        /* Try parsing as an integer */
        val = strtol(cp, &ep, 0);
        if (*cp == '\0' || *ep != '\0' || val < 0 || val > 255)
                return -1;
        return val;
}

const char *
iptos2str(int iptos)
{
        int i;
        static char iptos_str[sizeof "0xff"];

        for (i = 0; ipqos[i].name != NULL; i++) {
                if (ipqos[i].value == iptos)
                        return ipqos[i].name;
        }
        snprintf(iptos_str, sizeof iptos_str, "0x%02x", iptos);
        return iptos_str;
}

void
lowercase(char *s)
{
        for (; *s; s++)
                *s = tolower((u_char)*s);
}

int
unix_listener(const char *path, int backlog, int unlink_first)
{
        struct sockaddr_un sunaddr;
        int saved_errno, sock;

        memset(&sunaddr, 0, sizeof(sunaddr));
        sunaddr.sun_family = AF_UNIX;
        if (strlcpy(sunaddr.sun_path, path,
            sizeof(sunaddr.sun_path)) >= sizeof(sunaddr.sun_path)) {
                error_f("path \"%s\" too long for Unix domain socket", path);
                errno = ENAMETOOLONG;
                return -1;
        }

        sock = socket(PF_UNIX, SOCK_STREAM, 0);
        if (sock == -1) {
                saved_errno = errno;
                error_f("socket: %.100s", strerror(errno));
                errno = saved_errno;
                return -1;
        }
        if (unlink_first == 1) {
                if (unlink(path) != 0 && errno != ENOENT)
                        error("unlink(%s): %.100s", path, strerror(errno));
        }
        if (bind(sock, (struct sockaddr *)&sunaddr, sizeof(sunaddr)) == -1) {
                saved_errno = errno;
                error_f("cannot bind to path %s: %s", path, strerror(errno));
                close(sock);
                errno = saved_errno;
                return -1;
        }
        if (listen(sock, backlog) == -1) {
                saved_errno = errno;
                error_f("cannot listen on path %s: %s", path, strerror(errno));
                close(sock);
                unlink(path);
                errno = saved_errno;
                return -1;
        }
        return sock;
}

void
sock_set_v6only(int s)
{
#if defined(IPV6_V6ONLY) && !defined(__OpenBSD__)
        int on = 1;

        debug3("%s: set socket %d IPV6_V6ONLY", __func__, s);
        if (setsockopt(s, IPPROTO_IPV6, IPV6_V6ONLY, &on, sizeof(on)) == -1)
                error("setsockopt IPV6_V6ONLY: %s", strerror(errno));
#endif
}

/*
 * Compares two strings that maybe be NULL. Returns non-zero if strings
 * are both NULL or are identical, returns zero otherwise.
 */
static int
strcmp_maybe_null(const char *a, const char *b)
{
        if ((a == NULL && b != NULL) || (a != NULL && b == NULL))
                return 0;
        if (a != NULL && strcmp(a, b) != 0)
                return 0;
        return 1;
}

/*
 * Compare two forwards, returning non-zero if they are identical or
 * zero otherwise.
 */
int
forward_equals(const struct Forward *a, const struct Forward *b)
{
        if (strcmp_maybe_null(a->listen_host, b->listen_host) == 0)
                return 0;
        if (a->listen_port != b->listen_port)
                return 0;
        if (strcmp_maybe_null(a->listen_path, b->listen_path) == 0)
                return 0;
        if (strcmp_maybe_null(a->connect_host, b->connect_host) == 0)
                return 0;
        if (a->connect_port != b->connect_port)
                return 0;
        if (strcmp_maybe_null(a->connect_path, b->connect_path) == 0)
                return 0;
        /* allocated_port and handle are not checked */
        return 1;
}

/* returns 1 if process is already daemonized, 0 otherwise */
int
daemonized(void)
{
        int fd;

        if ((fd = open(_PATH_TTY, O_RDONLY | O_NOCTTY)) >= 0) {
                close(fd);
                return 0;       /* have controlling terminal */
        }
        if (getppid() != 1)
                return 0;       /* parent is not init */
        if (getsid(0) != getpid())
                return 0;       /* not session leader */
        debug3("already daemonized");
        return 1;
}

/*
 * Splits 's' into an argument vector. Handles quoted string and basic
 * escape characters (\\, \", \'). Caller must free the argument vector
 * and its members.
 */
int
argv_split(const char *s, int *argcp, char ***argvp, int terminate_on_comment)
{
        int r = SSH_ERR_INTERNAL_ERROR;
        int argc = 0, quote, i, j;
        char *arg, **argv = xcalloc(1, sizeof(*argv));

        *argvp = NULL;
        *argcp = 0;

        for (i = 0; s[i] != '\0'; i++) {
                /* Skip leading whitespace */
                if (s[i] == ' ' || s[i] == '\t')
                        continue;
                if (terminate_on_comment && s[i] == '#')
                        break;
                /* Start of a token */
                quote = 0;

                argv = xreallocarray(argv, (argc + 2), sizeof(*argv));
                arg = argv[argc++] = xcalloc(1, strlen(s + i) + 1);
                argv[argc] = NULL;

                /* Copy the token in, removing escapes */
                for (j = 0; s[i] != '\0'; i++) {
                        if (s[i] == '\\') {
                                if (s[i + 1] == '\'' ||
                                    s[i + 1] == '\"' ||
                                    s[i + 1] == '\\' ||
                                    (quote == 0 && s[i + 1] == ' ')) {
                                        i++; /* Skip '\' */
                                        arg[j++] = s[i];
                                } else {
                                        /* Unrecognised escape */
                                        arg[j++] = s[i];
                                }
                        } else if (quote == 0 && (s[i] == ' ' || s[i] == '\t'))
                                break; /* done */
                        else if (quote == 0 && (s[i] == '\"' || s[i] == '\''))
                                quote = s[i]; /* quote start */
                        else if (quote != 0 && s[i] == quote)
                                quote = 0; /* quote end */
                        else
                                arg[j++] = s[i];
                }
                if (s[i] == '\0') {
                        if (quote != 0) {
                                /* Ran out of string looking for close quote */
                                r = SSH_ERR_INVALID_FORMAT;
                                goto out;
                        }
                        break;
                }
        }
        /* Success */
        *argcp = argc;
        *argvp = argv;
        argc = 0;
        argv = NULL;
        r = 0;
 out:
        if (argc != 0 && argv != NULL) {
                for (i = 0; i < argc; i++)
                        free(argv[i]);
                free(argv);
        }
        return r;
}

/*
 * Reassemble an argument vector into a string, quoting and escaping as
 * necessary. Caller must free returned string.
 */
char *
argv_assemble(int argc, char **argv)
{
        int i, j, ws, r;
        char c, *ret;
        struct sshbuf *buf, *arg;

        if ((buf = sshbuf_new()) == NULL || (arg = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");

        for (i = 0; i < argc; i++) {
                ws = 0;
                sshbuf_reset(arg);
                for (j = 0; argv[i][j] != '\0'; j++) {
                        r = 0;
                        c = argv[i][j];
                        switch (c) {
                        case ' ':
                        case '\t':
                                ws = 1;
                                r = sshbuf_put_u8(arg, c);
                                break;
                        case '\\':
                        case '\'':
                        case '"':
                                if ((r = sshbuf_put_u8(arg, '\\')) != 0)
                                        break;
                                /* FALLTHROUGH */
                        default:
                                r = sshbuf_put_u8(arg, c);
                                break;
                        }
                        if (r != 0)
                                fatal_fr(r, "sshbuf_put_u8");
                }
                if ((i != 0 && (r = sshbuf_put_u8(buf, ' ')) != 0) ||
                    (ws != 0 && (r = sshbuf_put_u8(buf, '"')) != 0) ||
                    (r = sshbuf_putb(buf, arg)) != 0 ||
                    (ws != 0 && (r = sshbuf_put_u8(buf, '"')) != 0))
                        fatal_fr(r, "assemble");
        }
        if ((ret = malloc(sshbuf_len(buf) + 1)) == NULL)
                fatal_f("malloc failed");
        memcpy(ret, sshbuf_ptr(buf), sshbuf_len(buf));
        ret[sshbuf_len(buf)] = '\0';
        sshbuf_free(buf);
        sshbuf_free(arg);
        return ret;
}

char *
argv_next(int *argcp, char ***argvp)
{
        char *ret = (*argvp)[0];

        if (*argcp > 0 && ret != NULL) {
                (*argcp)--;
                (*argvp)++;
        }
        return ret;
}

void
argv_consume(int *argcp)
{
        *argcp = 0;
}

void
argv_free(char **av, int ac)
{
        int i;

        if (av == NULL)
                return;
        for (i = 0; i < ac; i++)
                free(av[i]);
        free(av);
}

/* Returns 0 if pid exited cleanly, non-zero otherwise */
int
exited_cleanly(pid_t pid, const char *tag, const char *cmd, int quiet)
{
        int status;

        while (waitpid(pid, &status, 0) == -1) {
                if (errno != EINTR) {
                        error("%s waitpid: %s", tag, strerror(errno));
                        return -1;
                }
        }
        if (WIFSIGNALED(status)) {
                error("%s %s exited on signal %d", tag, cmd, WTERMSIG(status));
                return -1;
        } else if (WEXITSTATUS(status) != 0) {
                do_log2(quiet ? SYSLOG_LEVEL_DEBUG1 : SYSLOG_LEVEL_INFO,
                    "%s %s failed, status %d", tag, cmd, WEXITSTATUS(status));
                return -1;
        }
        return 0;
}

/*
 * Check a given path for security. This is defined as all components
 * of the path to the file must be owned by either the owner of
 * of the file or root and no directories must be group or world writable.
 *
 * XXX Should any specific check be done for sym links ?
 *
 * Takes a file name, its stat information (preferably from fstat() to
 * avoid races), the uid of the expected owner, their home directory and an
 * error buffer plus max size as arguments.
 *
 * Returns 0 on success and -1 on failure
 */
int
safe_path(const char *name, struct stat *stp, const char *pw_dir,
    uid_t uid, char *err, size_t errlen)
{
        char buf[PATH_MAX], homedir[PATH_MAX];
        char *cp;
        int comparehome = 0;
        struct stat st;

        if (realpath(name, buf) == NULL) {
                snprintf(err, errlen, "realpath %s failed: %s", name,
                    strerror(errno));
                return -1;
        }
        if (pw_dir != NULL && realpath(pw_dir, homedir) != NULL)
                comparehome = 1;

        if (!S_ISREG(stp->st_mode)) {
                snprintf(err, errlen, "%s is not a regular file", buf);
                return -1;
        }
        if ((!platform_sys_dir_uid(stp->st_uid) && stp->st_uid != uid) ||
            (stp->st_mode & 022) != 0) {
                snprintf(err, errlen, "bad ownership or modes for file %s",
                    buf);
                return -1;
        }

        /* for each component of the canonical path, walking upwards */
        for (;;) {
                if ((cp = dirname(buf)) == NULL) {
                        snprintf(err, errlen, "dirname() failed");
                        return -1;
                }
                strlcpy(buf, cp, sizeof(buf));

                if (stat(buf, &st) == -1 ||
                    (!platform_sys_dir_uid(st.st_uid) && st.st_uid != uid) ||
                    (st.st_mode & 022) != 0) {
                        snprintf(err, errlen,
                            "bad ownership or modes for directory %s", buf);
                        return -1;
                }

                /* If are past the homedir then we can stop */
                if (comparehome && strcmp(homedir, buf) == 0)
                        break;

                /*
                 * dirname should always complete with a "/" path,
                 * but we can be paranoid and check for "." too
                 */
                if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0))
                        break;
        }
        return 0;
}

/*
 * Version of safe_path() that accepts an open file descriptor to
 * avoid races.
 *
 * Returns 0 on success and -1 on failure
 */
int
safe_path_fd(int fd, const char *file, struct passwd *pw,
    char *err, size_t errlen)
{
        struct stat st;

        /* check the open file to avoid races */
        if (fstat(fd, &st) == -1) {
                snprintf(err, errlen, "cannot stat file %s: %s",
                    file, strerror(errno));
                return -1;
        }
        return safe_path(file, &st, pw->pw_dir, pw->pw_uid, err, errlen);
}

/*
 * Sets the value of the given variable in the environment.  If the variable
 * already exists, its value is overridden.
 */
void
child_set_env(char ***envp, u_int *envsizep, const char *name,
        const char *value)
{
        char **env;
        u_int envsize;
        u_int i, namelen;

        if (strchr(name, '=') != NULL) {
                error("Invalid environment variable \"%.100s\"", name);
                return;
        }

        /*
         * If we're passed an uninitialized list, allocate a single null
         * entry before continuing.
         */
        if (*envp == NULL && *envsizep == 0) {
                *envp = xmalloc(sizeof(char *));
                *envp[0] = NULL;
                *envsizep = 1;
        }

        /*
         * Find the slot where the value should be stored.  If the variable
         * already exists, we reuse the slot; otherwise we append a new slot
         * at the end of the array, expanding if necessary.
         */
        env = *envp;
        namelen = strlen(name);
        for (i = 0; env[i]; i++)
                if (strncmp(env[i], name, namelen) == 0 && env[i][namelen] == '=')
                        break;
        if (env[i]) {
                /* Reuse the slot. */
                free(env[i]);
        } else {
                /* New variable.  Expand if necessary. */
                envsize = *envsizep;
                if (i >= envsize - 1) {
                        if (envsize >= 1000)
                                fatal("child_set_env: too many env vars");
                        envsize += 50;
                        env = (*envp) = xreallocarray(env, envsize, sizeof(char *));
                        *envsizep = envsize;
                }
                /* Need to set the NULL pointer at end of array beyond the new slot. */
                env[i + 1] = NULL;
        }

        /* Allocate space and format the variable in the appropriate slot. */
        /* XXX xasprintf */
        env[i] = xmalloc(strlen(name) + 1 + strlen(value) + 1);
        snprintf(env[i], strlen(name) + 1 + strlen(value) + 1, "%s=%s", name, value);
}

/*
 * Check and optionally lowercase a domain name, also removes trailing '.'
 * Returns 1 on success and 0 on failure, storing an error message in errstr.
 */
int
valid_domain(char *name, int makelower, const char **errstr)
{
        size_t i, l = strlen(name);
        u_char c, last = '\0';
        static char errbuf[256];

        if (l == 0) {
                strlcpy(errbuf, "empty domain name", sizeof(errbuf));
                goto bad;
        }
        if (!isalpha((u_char)name[0]) && !isdigit((u_char)name[0])) {
                snprintf(errbuf, sizeof(errbuf), "domain name \"%.100s\" "
                    "starts with invalid character", name);
                goto bad;
        }
        for (i = 0; i < l; i++) {
                c = tolower((u_char)name[i]);
                if (makelower)
                        name[i] = (char)c;
                if (last == '.' && c == '.') {
                        snprintf(errbuf, sizeof(errbuf), "domain name "
                            "\"%.100s\" contains consecutive separators", name);
                        goto bad;
                }
                if (c != '.' && c != '-' && !isalnum(c) &&
                    c != '_') /* technically invalid, but common */ {
                        snprintf(errbuf, sizeof(errbuf), "domain name "
                            "\"%.100s\" contains invalid characters", name);
                        goto bad;
                }
                last = c;
        }
        if (name[l - 1] == '.')
                name[l - 1] = '\0';
        if (errstr != NULL)
                *errstr = NULL;
        return 1;
bad:
        if (errstr != NULL)
                *errstr = errbuf;
        return 0;
}

/*
 * Verify that a environment variable name (not including initial '$') is
 * valid; consisting of one or more alphanumeric or underscore characters only.
 * Returns 1 on valid, 0 otherwise.
 */
int
valid_env_name(const char *name)
{
        const char *cp;

        if (name[0] == '\0')
                return 0;
        for (cp = name; *cp != '\0'; cp++) {
                if (!isalnum((u_char)*cp) && *cp != '_')
                        return 0;
        }
        return 1;
}

const char *
atoi_err(const char *nptr, int *val)
{
        const char *errstr = NULL;
        long long num;

        if (nptr == NULL || *nptr == '\0')
                return "missing";
        num = strtonum(nptr, 0, INT_MAX, &errstr);
        if (errstr == NULL)
                *val = (int)num;
        return errstr;
}

int
parse_absolute_time(const char *s, uint64_t *tp)
{
        struct tm tm;
        time_t tt;
        char buf[32], *fmt;

        *tp = 0;

        /*
         * POSIX strptime says "The application shall ensure that there
         * is white-space or other non-alphanumeric characters between
         * any two conversion specifications" so arrange things this way.
         */
        switch (strlen(s)) {
        case 8: /* YYYYMMDD */
                fmt = "%Y-%m-%d";
                snprintf(buf, sizeof(buf), "%.4s-%.2s-%.2s", s, s + 4, s + 6);
                break;
        case 12: /* YYYYMMDDHHMM */
                fmt = "%Y-%m-%dT%H:%M";
                snprintf(buf, sizeof(buf), "%.4s-%.2s-%.2sT%.2s:%.2s",
                    s, s + 4, s + 6, s + 8, s + 10);
                break;
        case 14: /* YYYYMMDDHHMMSS */
                fmt = "%Y-%m-%dT%H:%M:%S";
                snprintf(buf, sizeof(buf), "%.4s-%.2s-%.2sT%.2s:%.2s:%.2s",
                    s, s + 4, s + 6, s + 8, s + 10, s + 12);
                break;
        default:
                return SSH_ERR_INVALID_FORMAT;
        }

        memset(&tm, 0, sizeof(tm));
        if (strptime(buf, fmt, &tm) == NULL)
                return SSH_ERR_INVALID_FORMAT;
        if ((tt = mktime(&tm)) < 0)
                return SSH_ERR_INVALID_FORMAT;
        /* success */
        *tp = (uint64_t)tt;
        return 0;
}

/* On OpenBSD time_t is int64_t which is long long. */
/* #define SSH_TIME_T_MAX LLONG_MAX */

void
format_absolute_time(uint64_t t, char *buf, size_t len)
{
        time_t tt = t > SSH_TIME_T_MAX ? SSH_TIME_T_MAX : t;
        struct tm tm;

        localtime_r(&tt, &tm);
        strftime(buf, len, "%Y-%m-%dT%H:%M:%S", &tm);
}

/* check if path is absolute */
int
path_absolute(const char *path)
{
        return (*path == '/') ? 1 : 0;
}

void
skip_space(char **cpp)
{
        char *cp;

        for (cp = *cpp; *cp == ' ' || *cp == '\t'; cp++)
                ;
        *cpp = cp;
}

/* authorized_key-style options parsing helpers */

/*
 * Match flag 'opt' in *optsp, and if allow_negate is set then also match
 * 'no-opt'. Returns -1 if option not matched, 1 if option matches or 0
 * if negated option matches.
 * If the option or negated option matches, then *optsp is updated to
 * point to the first character after the option.
 */
int
opt_flag(const char *opt, int allow_negate, const char **optsp)
{
        size_t opt_len = strlen(opt);
        const char *opts = *optsp;
        int negate = 0;

        if (allow_negate && strncasecmp(opts, "no-", 3) == 0) {
                opts += 3;
                negate = 1;
        }
        if (strncasecmp(opts, opt, opt_len) == 0) {
                *optsp = opts + opt_len;
                return negate ? 0 : 1;
        }
        return -1;
}

char *
opt_dequote(const char **sp, const char **errstrp)
{
        const char *s = *sp;
        char *ret;
        size_t i;

        *errstrp = NULL;
        if (*s != '"') {
                *errstrp = "missing start quote";
                return NULL;
        }
        s++;
        if ((ret = malloc(strlen((s)) + 1)) == NULL) {
                *errstrp = "memory allocation failed";
                return NULL;
        }
        for (i = 0; *s != '\0' && *s != '"';) {
                if (s[0] == '\\' && s[1] == '"')
                        s++;
                ret[i++] = *s++;
        }
        if (*s == '\0') {
                *errstrp = "missing end quote";
                free(ret);
                return NULL;
        }
        ret[i] = '\0';
        s++;
        *sp = s;
        return ret;
}

int
opt_match(const char **opts, const char *term)
{
        if (strncasecmp((*opts), term, strlen(term)) == 0 &&
            (*opts)[strlen(term)] == '=') {
                *opts += strlen(term) + 1;
                return 1;
        }
        return 0;
}

void
opt_array_append2(const char *file, const int line, const char *directive,
    char ***array, int **iarray, u_int *lp, const char *s, int i)
{

        if (*lp >= INT_MAX)
                fatal("%s line %d: Too many %s entries", file, line, directive);

        if (iarray != NULL) {
                *iarray = xrecallocarray(*iarray, *lp, *lp + 1,
                    sizeof(**iarray));
                (*iarray)[*lp] = i;
        }

        *array = xrecallocarray(*array, *lp, *lp + 1, sizeof(**array));
        (*array)[*lp] = xstrdup(s);
        (*lp)++;
}

void
opt_array_append(const char *file, const int line, const char *directive,
    char ***array, u_int *lp, const char *s)
{
        opt_array_append2(file, line, directive, array, NULL, lp, s, 0);
}

sshsig_t
ssh_signal(int signum, sshsig_t handler)
{
        struct sigaction sa, osa;

        /* mask all other signals while in handler */
        memset(&sa, 0, sizeof(sa));
        sa.sa_handler = handler;
        sigfillset(&sa.sa_mask);
#if defined(SA_RESTART) && !defined(NO_SA_RESTART)
        if (signum != SIGALRM)
                sa.sa_flags = SA_RESTART;
#endif
        if (sigaction(signum, &sa, &osa) == -1) {
                debug3("sigaction(%s): %s", strsignal(signum), strerror(errno));
                return SIG_ERR;
        }
        return osa.sa_handler;
}

int
stdfd_devnull(int do_stdin, int do_stdout, int do_stderr)
{
        int devnull, ret = 0;

        if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
                error_f("open %s: %s", _PATH_DEVNULL,
                    strerror(errno));
                return -1;
        }
        if ((do_stdin && dup2(devnull, STDIN_FILENO) == -1) ||
            (do_stdout && dup2(devnull, STDOUT_FILENO) == -1) ||
            (do_stderr && dup2(devnull, STDERR_FILENO) == -1)) {
                error_f("dup2: %s", strerror(errno));
                ret = -1;
        }
        if (devnull > STDERR_FILENO)
                close(devnull);
        return ret;
}

/*
 * Runs command in a subprocess with a minimal environment.
 * Returns pid on success, 0 on failure.
 * The child stdout and stderr maybe captured, left attached or sent to
 * /dev/null depending on the contents of flags.
 * "tag" is prepended to log messages.
 * NB. "command" is only used for logging; the actual command executed is
 * av[0].
 */
pid_t
subprocess(const char *tag, const char *command,
    int ac, char **av, FILE **child, u_int flags,
    struct passwd *pw, privdrop_fn *drop_privs, privrestore_fn *restore_privs)
{
        FILE *f = NULL;
        struct stat st;
        int fd, devnull, p[2], i;
        pid_t pid;
        char *cp, errmsg[512];
        u_int nenv = 0;
        char **env = NULL;

        /* If dropping privs, then must specify user and restore function */
        if (drop_privs != NULL && (pw == NULL || restore_privs == NULL)) {
                error("%s: inconsistent arguments", tag); /* XXX fatal? */
                return 0;
        }
        if (pw == NULL && (pw = getpwuid(getuid())) == NULL) {
                error("%s: no user for current uid", tag);
                return 0;
        }
        if (child != NULL)
                *child = NULL;

        debug3_f("%s command \"%s\" running as %s (flags 0x%x)",
            tag, command, pw->pw_name, flags);

        /* Check consistency */
        if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0 &&
            (flags & SSH_SUBPROCESS_STDOUT_CAPTURE) != 0) {
                error_f("inconsistent flags");
                return 0;
        }
        if (((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) == 0) != (child == NULL)) {
                error_f("inconsistent flags/output");
                return 0;
        }

        /*
         * If executing an explicit binary, then verify the it exists
         * and appears safe-ish to execute
         */
        if (!path_absolute(av[0])) {
                error("%s path is not absolute", tag);
                return 0;
        }
        if (drop_privs != NULL)
                drop_privs(pw);
        if (stat(av[0], &st) == -1) {
                error("Could not stat %s \"%s\": %s", tag,
                    av[0], strerror(errno));
                goto restore_return;
        }
        if ((flags & SSH_SUBPROCESS_UNSAFE_PATH) == 0 &&
            safe_path(av[0], &st, NULL, 0, errmsg, sizeof(errmsg)) != 0) {
                error("Unsafe %s \"%s\": %s", tag, av[0], errmsg);
                goto restore_return;
        }
        /* Prepare to keep the child's stdout if requested */
        if (pipe(p) == -1) {
                error("%s: pipe: %s", tag, strerror(errno));
 restore_return:
                if (restore_privs != NULL)
                        restore_privs();
                return 0;
        }
        if (restore_privs != NULL)
                restore_privs();

        switch ((pid = fork())) {
        case -1: /* error */
                error("%s: fork: %s", tag, strerror(errno));
                close(p[0]);
                close(p[1]);
                return 0;
        case 0: /* child */
                /* Prepare a minimal environment for the child. */
                if ((flags & SSH_SUBPROCESS_PRESERVE_ENV) == 0) {
                        nenv = 5;
                        env = xcalloc(sizeof(*env), nenv);
                        child_set_env(&env, &nenv, "PATH", _PATH_STDPATH);
                        child_set_env(&env, &nenv, "USER", pw->pw_name);
                        child_set_env(&env, &nenv, "LOGNAME", pw->pw_name);
                        child_set_env(&env, &nenv, "HOME", pw->pw_dir);
                        if ((cp = getenv("LANG")) != NULL)
                                child_set_env(&env, &nenv, "LANG", cp);
                }

                for (i = 1; i < NSIG; i++)
                        ssh_signal(i, SIG_DFL);

                if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
                        error("%s: open %s: %s", tag, _PATH_DEVNULL,
                            strerror(errno));
                        _exit(1);
                }
                if (dup2(devnull, STDIN_FILENO) == -1) {
                        error("%s: dup2: %s", tag, strerror(errno));
                        _exit(1);
                }

                /* Set up stdout as requested; leave stderr in place for now. */
                fd = -1;
                if ((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) != 0)
                        fd = p[1];
                else if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0)
                        fd = devnull;
                if (fd != -1 && dup2(fd, STDOUT_FILENO) == -1) {
                        error("%s: dup2: %s", tag, strerror(errno));
                        _exit(1);
                }
                closefrom(STDERR_FILENO + 1);

                if (geteuid() == 0 &&
                    initgroups(pw->pw_name, pw->pw_gid) == -1) {
                        error("%s: initgroups(%s, %u): %s", tag,
                            pw->pw_name, (u_int)pw->pw_gid, strerror(errno));
                        _exit(1);
                }
                if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) == -1) {
                        error("%s: setresgid %u: %s", tag, (u_int)pw->pw_gid,
                            strerror(errno));
                        _exit(1);
                }
                if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) == -1) {
                        error("%s: setresuid %u: %s", tag, (u_int)pw->pw_uid,
                            strerror(errno));
                        _exit(1);
                }
                /* stdin is pointed to /dev/null at this point */
                if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0 &&
                    dup2(STDIN_FILENO, STDERR_FILENO) == -1) {
                        error("%s: dup2: %s", tag, strerror(errno));
                        _exit(1);
                }
                if (env != NULL)
                        execve(av[0], av, env);
                else
                        execv(av[0], av);
                error("%s %s \"%s\": %s", tag, env == NULL ? "execv" : "execve",
                    command, strerror(errno));
                _exit(127);
        default: /* parent */
                break;
        }

        close(p[1]);
        if ((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) == 0)
                close(p[0]);
        else if ((f = fdopen(p[0], "r")) == NULL) {
                error("%s: fdopen: %s", tag, strerror(errno));
                close(p[0]);
                /* Don't leave zombie child */
                kill(pid, SIGTERM);
                while (waitpid(pid, NULL, 0) == -1 && errno == EINTR)
                        ;
                return 0;
        }
        /* Success */
        debug3_f("%s pid %ld", tag, (long)pid);
        if (child != NULL)
                *child = f;
        return pid;
}

const char *
lookup_env_in_list(const char *env, char * const *envs, size_t nenvs)
{
        size_t i, envlen;

        envlen = strlen(env);
        for (i = 0; i < nenvs; i++) {
                if (strncmp(envs[i], env, envlen) == 0 &&
                    envs[i][envlen] == '=') {
                        return envs[i] + envlen + 1;
                }
        }
        return NULL;
}