Merge branch 'master' of git://bogomips.org/git-svn

[git.git] / daemon.c

#include "cache.h"
#include "pkt-line.h"
#include "exec_cmd.h"
#include "run-command.h"
#include "strbuf.h"
#include "string-list.h"

#ifndef HOST_NAME_MAX
#define HOST_NAME_MAX 256
#endif

#ifdef NO_INITGROUPS
#define initgroups(x, y) (0) /* nothing */
#endif

static int log_syslog;
static int verbose;
static int reuseaddr;
static int informative_errors;

static const char daemon_usage[] =
"git daemon [--verbose] [--syslog] [--export-all]\n"
"           [--timeout=<n>] [--init-timeout=<n>] [--max-connections=<n>]\n"
"           [--strict-paths] [--base-path=<path>] [--base-path-relaxed]\n"
"           [--user-path | --user-path=<path>]\n"
"           [--interpolated-path=<path>]\n"
"           [--reuseaddr] [--pid-file=<file>]\n"
"           [--(enable|disable|allow-override|forbid-override)=<service>]\n"
"           [--access-hook=<path>]\n"
"           [--inetd | [--listen=<host_or_ipaddr>] [--port=<n>]\n"
"                      [--detach] [--user=<user> [--group=<group>]]\n"
"           [<directory>...]";

/* List of acceptable pathname prefixes */
static char **ok_paths;
static int strict_paths;

/* If this is set, git-daemon-export-ok is not required */
static int export_all_trees;

/* Take all paths relative to this one if non-NULL */
static const char *base_path;
static const char *interpolated_path;
static int base_path_relaxed;

/* If defined, ~user notation is allowed and the string is inserted
 * after ~user/.  E.g. a request to git://host/~alice/frotz would
 * go to /home/alice/pub_git/frotz with --user-path=pub_git.
 */
static const char *user_path;

/* Timeout, and initial timeout */
static unsigned int timeout;
static unsigned int init_timeout;

struct hostinfo {
        struct strbuf hostname;
        struct strbuf canon_hostname;
        struct strbuf ip_address;
        struct strbuf tcp_port;
        unsigned int hostname_lookup_done:1;
        unsigned int saw_extended_args:1;
};

static void lookup_hostname(struct hostinfo *hi);

static const char *get_canon_hostname(struct hostinfo *hi)
{
        lookup_hostname(hi);
        return hi->canon_hostname.buf;
}

static const char *get_ip_address(struct hostinfo *hi)
{
        lookup_hostname(hi);
        return hi->ip_address.buf;
}

static void logreport(int priority, const char *err, va_list params)
{
        if (log_syslog) {
                char buf[1024];
                vsnprintf(buf, sizeof(buf), err, params);
                syslog(priority, "%s", buf);
        } else {
                /*
                 * Since stderr is set to buffered mode, the
                 * logging of different processes will not overlap
                 * unless they overflow the (rather big) buffers.
                 */
                fprintf(stderr, "[%"PRIuMAX"] ", (uintmax_t)getpid());
                vfprintf(stderr, err, params);
                fputc('\n', stderr);
                fflush(stderr);
        }
}

__attribute__((format (printf, 1, 2)))
static void logerror(const char *err, ...)
{
        va_list params;
        va_start(params, err);
        logreport(LOG_ERR, err, params);
        va_end(params);
}

__attribute__((format (printf, 1, 2)))
static void loginfo(const char *err, ...)
{
        va_list params;
        if (!verbose)
                return;
        va_start(params, err);
        logreport(LOG_INFO, err, params);
        va_end(params);
}

static void NORETURN daemon_die(const char *err, va_list params)
{
        logreport(LOG_ERR, err, params);
        exit(1);
}

struct expand_path_context {
        const char *directory;
        struct hostinfo *hostinfo;
};

static size_t expand_path(struct strbuf *sb, const char *placeholder, void *ctx)
{
        struct expand_path_context *context = ctx;
        struct hostinfo *hi = context->hostinfo;

        switch (placeholder[0]) {
        case 'H':
                strbuf_addbuf(sb, &hi->hostname);
                return 1;
        case 'C':
                if (placeholder[1] == 'H') {
                        strbuf_addstr(sb, get_canon_hostname(hi));
                        return 2;
                }
                break;
        case 'I':
                if (placeholder[1] == 'P') {
                        strbuf_addstr(sb, get_ip_address(hi));
                        return 2;
                }
                break;
        case 'P':
                strbuf_addbuf(sb, &hi->tcp_port);
                return 1;
        case 'D':
                strbuf_addstr(sb, context->directory);
                return 1;
        }
        return 0;
}

static const char *path_ok(const char *directory, struct hostinfo *hi)
{
        static char rpath[PATH_MAX];
        static char interp_path[PATH_MAX];
        const char *path;
        const char *dir;

        dir = directory;

        if (daemon_avoid_alias(dir)) {
                logerror("'%s': aliased", dir);
                return NULL;
        }

        if (*dir == '~') {
                if (!user_path) {
                        logerror("'%s': User-path not allowed", dir);
                        return NULL;
                }
                if (*user_path) {
                        /* Got either "~alice" or "~alice/foo";
                         * rewrite them to "~alice/%s" or
                         * "~alice/%s/foo".
                         */
                        int namlen, restlen = strlen(dir);
                        const char *slash = strchr(dir, '/');
                        if (!slash)
                                slash = dir + restlen;
                        namlen = slash - dir;
                        restlen -= namlen;
                        loginfo("userpath <%s>, request <%s>, namlen %d, restlen %d, slash <%s>", user_path, dir, namlen, restlen, slash);
                        snprintf(rpath, PATH_MAX, "%.*s/%s%.*s",
                                 namlen, dir, user_path, restlen, slash);
                        dir = rpath;
                }
        }
        else if (interpolated_path && hi->saw_extended_args) {
                struct strbuf expanded_path = STRBUF_INIT;
                struct expand_path_context context;

                context.directory = directory;
                context.hostinfo = hi;

                if (*dir != '/') {
                        /* Allow only absolute */
                        logerror("'%s': Non-absolute path denied (interpolated-path active)", dir);
                        return NULL;
                }

                strbuf_expand(&expanded_path, interpolated_path,
                              expand_path, &context);
                strlcpy(interp_path, expanded_path.buf, PATH_MAX);
                strbuf_release(&expanded_path);
                loginfo("Interpolated dir '%s'", interp_path);

                dir = interp_path;
        }
        else if (base_path) {
                if (*dir != '/') {
                        /* Allow only absolute */
                        logerror("'%s': Non-absolute path denied (base-path active)", dir);
                        return NULL;
                }
                snprintf(rpath, PATH_MAX, "%s%s", base_path, dir);
                dir = rpath;
        }

        path = enter_repo(dir, strict_paths);
        if (!path && base_path && base_path_relaxed) {
                /*
                 * if we fail and base_path_relaxed is enabled, try without
                 * prefixing the base path
                 */
                dir = directory;
                path = enter_repo(dir, strict_paths);
        }

        if (!path) {
                logerror("'%s' does not appear to be a git repository", dir);
                return NULL;
        }

        if ( ok_paths && *ok_paths ) {
                char **pp;
                int pathlen = strlen(path);

                /* The validation is done on the paths after enter_repo
                 * appends optional {.git,.git/.git} and friends, but
                 * it does not use getcwd().  So if your /pub is
                 * a symlink to /mnt/pub, you can whitelist /pub and
                 * do not have to say /mnt/pub.
                 * Do not say /pub/.
                 */
                for ( pp = ok_paths ; *pp ; pp++ ) {
                        int len = strlen(*pp);
                        if (len <= pathlen &&
                            !memcmp(*pp, path, len) &&
                            (path[len] == '\0' ||
                             (!strict_paths && path[len] == '/')))
                                return path;
                }
        }
        else {
                /* be backwards compatible */
                if (!strict_paths)
                        return path;
        }

        logerror("'%s': not in whitelist", path);
        return NULL;            /* Fallthrough. Deny by default */
}

typedef int (*daemon_service_fn)(void);
struct daemon_service {
        const char *name;
        const char *config_name;
        daemon_service_fn fn;
        int enabled;
        int overridable;
};

static int daemon_error(const char *dir, const char *msg)
{
        if (!informative_errors)
                msg = "access denied or repository not exported";
        packet_write(1, "ERR %s: %s", msg, dir);
        return -1;
}

static const char *access_hook;

static int run_access_hook(struct daemon_service *service, const char *dir,
                           const char *path, struct hostinfo *hi)
{
        struct child_process child = CHILD_PROCESS_INIT;
        struct strbuf buf = STRBUF_INIT;
        const char *argv[8];
        const char **arg = argv;
        char *eol;
        int seen_errors = 0;

        *arg++ = access_hook;
        *arg++ = service->name;
        *arg++ = path;
        *arg++ = hi->hostname.buf;
        *arg++ = get_canon_hostname(hi);
        *arg++ = get_ip_address(hi);
        *arg++ = hi->tcp_port.buf;
        *arg = NULL;

        child.use_shell = 1;
        child.argv = argv;
        child.no_stdin = 1;
        child.no_stderr = 1;
        child.out = -1;
        if (start_command(&child)) {
                logerror("daemon access hook '%s' failed to start",
                         access_hook);
                goto error_return;
        }
        if (strbuf_read(&buf, child.out, 0) < 0) {
                logerror("failed to read from pipe to daemon access hook '%s'",
                         access_hook);
                strbuf_reset(&buf);
                seen_errors = 1;
        }
        if (close(child.out) < 0) {
                logerror("failed to close pipe to daemon access hook '%s'",
                         access_hook);
                seen_errors = 1;
        }
        if (finish_command(&child))
                seen_errors = 1;

        if (!seen_errors) {
                strbuf_release(&buf);
                return 0;
        }

error_return:
        strbuf_ltrim(&buf);
        if (!buf.len)
                strbuf_addstr(&buf, "service rejected");
        eol = strchr(buf.buf, '\n');
        if (eol)
                *eol = '\0';
        errno = EACCES;
        daemon_error(dir, buf.buf);
        strbuf_release(&buf);
        return -1;
}

static int run_service(const char *dir, struct daemon_service *service,
                       struct hostinfo *hi)
{
        const char *path;
        int enabled = service->enabled;
        struct strbuf var = STRBUF_INIT;

        loginfo("Request %s for '%s'", service->name, dir);

        if (!enabled && !service->overridable) {
                logerror("'%s': service not enabled.", service->name);
                errno = EACCES;
                return daemon_error(dir, "service not enabled");
        }

        if (!(path = path_ok(dir, hi)))
                return daemon_error(dir, "no such repository");

        /*
         * Security on the cheap.
         *
         * We want a readable HEAD, usable "objects" directory, and
         * a "git-daemon-export-ok" flag that says that the other side
         * is ok with us doing this.
         *
         * path_ok() uses enter_repo() and does whitelist checking.
         * We only need to make sure the repository is exported.
         */

        if (!export_all_trees && access("git-daemon-export-ok", F_OK)) {
                logerror("'%s': repository not exported.", path);
                errno = EACCES;
                return daemon_error(dir, "repository not exported");
        }

        if (service->overridable) {
                strbuf_addf(&var, "daemon.%s", service->config_name);
                git_config_get_bool(var.buf, &enabled);
                strbuf_release(&var);
        }
        if (!enabled) {
                logerror("'%s': service not enabled for '%s'",
                         service->name, path);
                errno = EACCES;
                return daemon_error(dir, "service not enabled");
        }

        /*
         * Optionally, a hook can choose to deny access to the
         * repository depending on the phase of the moon.
         */
        if (access_hook && run_access_hook(service, dir, path, hi))
                return -1;

        /*
         * We'll ignore SIGTERM from now on, we have a
         * good client.
         */
        signal(SIGTERM, SIG_IGN);

        return service->fn();
}

static void copy_to_log(int fd)
{
        struct strbuf line = STRBUF_INIT;
        FILE *fp;

        fp = fdopen(fd, "r");
        if (fp == NULL) {
                logerror("fdopen of error channel failed");
                close(fd);
                return;
        }

        while (strbuf_getline_lf(&line, fp) != EOF) {
                logerror("%s", line.buf);
                strbuf_setlen(&line, 0);
        }

        strbuf_release(&line);
        fclose(fp);
}

static int run_service_command(const char **argv)
{
        struct child_process cld = CHILD_PROCESS_INIT;

        cld.argv = argv;
        cld.git_cmd = 1;
        cld.err = -1;
        if (start_command(&cld))
                return -1;

        close(0);
        close(1);

        copy_to_log(cld.err);

        return finish_command(&cld);
}

static int upload_pack(void)
{
        /* Timeout as string */
        char timeout_buf[64];
        const char *argv[] = { "upload-pack", "--strict", NULL, ".", NULL };

        argv[2] = timeout_buf;

        snprintf(timeout_buf, sizeof timeout_buf, "--timeout=%u", timeout);
        return run_service_command(argv);
}

static int upload_archive(void)
{
        static const char *argv[] = { "upload-archive", ".", NULL };
        return run_service_command(argv);
}

static int receive_pack(void)
{
        static const char *argv[] = { "receive-pack", ".", NULL };
        return run_service_command(argv);
}

static struct daemon_service daemon_service[] = {
        { "upload-archive", "uploadarch", upload_archive, 0, 1 },
        { "upload-pack", "uploadpack", upload_pack, 1, 1 },
        { "receive-pack", "receivepack", receive_pack, 0, 1 },
};

static void enable_service(const char *name, int ena)
{
        int i;
        for (i = 0; i < ARRAY_SIZE(daemon_service); i++) {
                if (!strcmp(daemon_service[i].name, name)) {
                        daemon_service[i].enabled = ena;
                        return;
                }
        }
        die("No such service %s", name);
}

static void make_service_overridable(const char *name, int ena)
{
        int i;
        for (i = 0; i < ARRAY_SIZE(daemon_service); i++) {
                if (!strcmp(daemon_service[i].name, name)) {
                        daemon_service[i].overridable = ena;
                        return;
                }
        }
        die("No such service %s", name);
}

static void parse_host_and_port(char *hostport, char **host,
        char **port)
{
        if (*hostport == '[') {
                char *end;

                end = strchr(hostport, ']');
                if (!end)
                        die("Invalid request ('[' without ']')");
                *end = '\0';
                *host = hostport + 1;
                if (!end[1])
                        *port = NULL;
                else if (end[1] == ':')
                        *port = end + 2;
                else
                        die("Garbage after end of host part");
        } else {
                *host = hostport;
                *port = strrchr(hostport, ':');
                if (*port) {
                        **port = '\0';
                        ++*port;
                }
        }
}

/*
 * Sanitize a string from the client so that it's OK to be inserted into a
 * filesystem path. Specifically, we disallow slashes, runs of "..", and
 * trailing and leading dots, which means that the client cannot escape
 * our base path via ".." traversal.
 */
static void sanitize_client(struct strbuf *out, const char *in)
{
        for (; *in; in++) {
                if (*in == '/')
                        continue;
                if (*in == '.' && (!out->len || out->buf[out->len - 1] == '.'))
                        continue;
                strbuf_addch(out, *in);
        }

        while (out->len && out->buf[out->len - 1] == '.')
                strbuf_setlen(out, out->len - 1);
}

/*
 * Like sanitize_client, but we also perform any canonicalization
 * to make life easier on the admin.
 */
static void canonicalize_client(struct strbuf *out, const char *in)
{
        sanitize_client(out, in);
        strbuf_tolower(out);
}

/*
 * Read the host as supplied by the client connection.
 */
static void parse_host_arg(struct hostinfo *hi, char *extra_args, int buflen)
{
        char *val;
        int vallen;
        char *end = extra_args + buflen;

        if (extra_args < end && *extra_args) {
                hi->saw_extended_args = 1;
                if (strncasecmp("host=", extra_args, 5) == 0) {
                        val = extra_args + 5;
                        vallen = strlen(val) + 1;
                        if (*val) {
                                /* Split <host>:<port> at colon. */
                                char *host;
                                char *port;
                                parse_host_and_port(val, &host, &port);
                                if (port)
                                        sanitize_client(&hi->tcp_port, port);
                                canonicalize_client(&hi->hostname, host);
                                hi->hostname_lookup_done = 0;
                        }

                        /* On to the next one */
                        extra_args = val + vallen;
                }
                if (extra_args < end && *extra_args)
                        die("Invalid request");
        }
}

/*
 * Locate canonical hostname and its IP address.
 */
static void lookup_hostname(struct hostinfo *hi)
{
        if (!hi->hostname_lookup_done && hi->hostname.len) {
#ifndef NO_IPV6
                struct addrinfo hints;
                struct addrinfo *ai;
                int gai;
                static char addrbuf[HOST_NAME_MAX + 1];

                memset(&hints, 0, sizeof(hints));
                hints.ai_flags = AI_CANONNAME;

                gai = getaddrinfo(hi->hostname.buf, NULL, &hints, &ai);
                if (!gai) {
                        struct sockaddr_in *sin_addr = (void *)ai->ai_addr;

                        inet_ntop(AF_INET, &sin_addr->sin_addr,
                                  addrbuf, sizeof(addrbuf));
                        strbuf_addstr(&hi->ip_address, addrbuf);

                        if (ai->ai_canonname)
                                sanitize_client(&hi->canon_hostname,
                                                ai->ai_canonname);
                        else
                                strbuf_addbuf(&hi->canon_hostname,
                                              &hi->ip_address);

                        freeaddrinfo(ai);
                }
#else
                struct hostent *hent;
                struct sockaddr_in sa;
                char **ap;
                static char addrbuf[HOST_NAME_MAX + 1];

                hent = gethostbyname(hi->hostname.buf);
                if (hent) {
                        ap = hent->h_addr_list;
                        memset(&sa, 0, sizeof sa);
                        sa.sin_family = hent->h_addrtype;
                        sa.sin_port = htons(0);
                        memcpy(&sa.sin_addr, *ap, hent->h_length);

                        inet_ntop(hent->h_addrtype, &sa.sin_addr,
                                  addrbuf, sizeof(addrbuf));

                        sanitize_client(&hi->canon_hostname, hent->h_name);
                        strbuf_addstr(&hi->ip_address, addrbuf);
                }
#endif
                hi->hostname_lookup_done = 1;
        }
}

static void hostinfo_init(struct hostinfo *hi)
{
        memset(hi, 0, sizeof(*hi));
        strbuf_init(&hi->hostname, 0);
        strbuf_init(&hi->canon_hostname, 0);
        strbuf_init(&hi->ip_address, 0);
        strbuf_init(&hi->tcp_port, 0);
}

static void hostinfo_clear(struct hostinfo *hi)
{
        strbuf_release(&hi->hostname);
        strbuf_release(&hi->canon_hostname);
        strbuf_release(&hi->ip_address);
        strbuf_release(&hi->tcp_port);
}

static void set_keep_alive(int sockfd)
{
        int ka = 1;

        if (setsockopt(sockfd, SOL_SOCKET, SO_KEEPALIVE, &ka, sizeof(ka)) < 0)
                logerror("unable to set SO_KEEPALIVE on socket: %s",
                        strerror(errno));
}

static int execute(void)
{
        char *line = packet_buffer;
        int pktlen, len, i;
        char *addr = getenv("REMOTE_ADDR"), *port = getenv("REMOTE_PORT");
        struct hostinfo hi;

        hostinfo_init(&hi);

        if (addr)
                loginfo("Connection from %s:%s", addr, port);

        set_keep_alive(0);
        alarm(init_timeout ? init_timeout : timeout);
        pktlen = packet_read(0, NULL, NULL, packet_buffer, sizeof(packet_buffer), 0);
        alarm(0);

        len = strlen(line);
        if (pktlen != len)
                loginfo("Extended attributes (%d bytes) exist <%.*s>",
                        (int) pktlen - len,
                        (int) pktlen - len, line + len + 1);
        if (len && line[len-1] == '\n') {
                line[--len] = 0;
                pktlen--;
        }

        if (len != pktlen)
                parse_host_arg(&hi, line + len + 1, pktlen - len - 1);

        for (i = 0; i < ARRAY_SIZE(daemon_service); i++) {
                struct daemon_service *s = &(daemon_service[i]);
                const char *arg;

                if (skip_prefix(line, "git-", &arg) &&
                    skip_prefix(arg, s->name, &arg) &&
                    *arg++ == ' ') {
                        /*
                         * Note: The directory here is probably context sensitive,
                         * and might depend on the actual service being performed.
                         */
                        int rc = run_service(arg, s, &hi);
                        hostinfo_clear(&hi);
                        return rc;
                }
        }

        hostinfo_clear(&hi);
        logerror("Protocol error: '%s'", line);
        return -1;
}

static int addrcmp(const struct sockaddr_storage *s1,
    const struct sockaddr_storage *s2)
{
        const struct sockaddr *sa1 = (const struct sockaddr*) s1;
        const struct sockaddr *sa2 = (const struct sockaddr*) s2;

        if (sa1->sa_family != sa2->sa_family)
                return sa1->sa_family - sa2->sa_family;
        if (sa1->sa_family == AF_INET)
                return memcmp(&((struct sockaddr_in *)s1)->sin_addr,
                    &((struct sockaddr_in *)s2)->sin_addr,
                    sizeof(struct in_addr));
#ifndef NO_IPV6
        if (sa1->sa_family == AF_INET6)
                return memcmp(&((struct sockaddr_in6 *)s1)->sin6_addr,
                    &((struct sockaddr_in6 *)s2)->sin6_addr,
                    sizeof(struct in6_addr));
#endif
        return 0;
}

static int max_connections = 32;

static unsigned int live_children;

static struct child {
        struct child *next;
        struct child_process cld;
        struct sockaddr_storage address;
} *firstborn;

static void add_child(struct child_process *cld, struct sockaddr *addr, socklen_t addrlen)
{
        struct child *newborn, **cradle;

        newborn = xcalloc(1, sizeof(*newborn));
        live_children++;
        memcpy(&newborn->cld, cld, sizeof(*cld));
        memcpy(&newborn->address, addr, addrlen);
        for (cradle = &firstborn; *cradle; cradle = &(*cradle)->next)
                if (!addrcmp(&(*cradle)->address, &newborn->address))
                        break;
        newborn->next = *cradle;
        *cradle = newborn;
}

/*
 * This gets called if the number of connections grows
 * past "max_connections".
 *
 * We kill the newest connection from a duplicate IP.
 */
static void kill_some_child(void)
{
        const struct child *blanket, *next;

        if (!(blanket = firstborn))
                return;

        for (; (next = blanket->next); blanket = next)
                if (!addrcmp(&blanket->address, &next->address)) {
                        kill(blanket->cld.pid, SIGTERM);
                        break;
                }
}

static void check_dead_children(void)
{
        int status;
        pid_t pid;

        struct child **cradle, *blanket;
        for (cradle = &firstborn; (blanket = *cradle);)
                if ((pid = waitpid(blanket->cld.pid, &status, WNOHANG)) > 1) {
                        const char *dead = "";
                        if (status)
                                dead = " (with error)";
                        loginfo("[%"PRIuMAX"] Disconnected%s", (uintmax_t)pid, dead);

                        /* remove the child */
                        *cradle = blanket->next;
                        live_children--;
                        child_process_clear(&blanket->cld);
                        free(blanket);
                } else
                        cradle = &blanket->next;
}

static struct argv_array cld_argv = ARGV_ARRAY_INIT;
static void handle(int incoming, struct sockaddr *addr, socklen_t addrlen)
{
        struct child_process cld = CHILD_PROCESS_INIT;

        if (max_connections && live_children >= max_connections) {
                kill_some_child();
                sleep(1);  /* give it some time to die */
                check_dead_children();
                if (live_children >= max_connections) {
                        close(incoming);
                        logerror("Too many children, dropping connection");
                        return;
                }
        }

        if (addr->sa_family == AF_INET) {
                char buf[128] = "";
                struct sockaddr_in *sin_addr = (void *) addr;
                inet_ntop(addr->sa_family, &sin_addr->sin_addr, buf, sizeof(buf));
                argv_array_pushf(&cld.env_array, "REMOTE_ADDR=%s", buf);
                argv_array_pushf(&cld.env_array, "REMOTE_PORT=%d",
                                 ntohs(sin_addr->sin_port));
#ifndef NO_IPV6
        } else if (addr->sa_family == AF_INET6) {
                char buf[128] = "";
                struct sockaddr_in6 *sin6_addr = (void *) addr;
                inet_ntop(AF_INET6, &sin6_addr->sin6_addr, buf, sizeof(buf));
                argv_array_pushf(&cld.env_array, "REMOTE_ADDR=[%s]", buf);
                argv_array_pushf(&cld.env_array, "REMOTE_PORT=%d",
                                 ntohs(sin6_addr->sin6_port));
#endif
        }

        cld.argv = cld_argv.argv;
        cld.in = incoming;
        cld.out = dup(incoming);

        if (start_command(&cld))
                logerror("unable to fork");
        else
                add_child(&cld, addr, addrlen);
}

static void child_handler(int signo)
{
        /*
         * Otherwise empty handler because systemcalls will get interrupted
         * upon signal receipt
         * SysV needs the handler to be rearmed
         */
        signal(SIGCHLD, child_handler);
}

static int set_reuse_addr(int sockfd)
{
        int on = 1;

        if (!reuseaddr)
                return 0;
        return setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR,
                          &on, sizeof(on));
}

struct socketlist {
        int *list;
        size_t nr;
        size_t alloc;
};

static const char *ip2str(int family, struct sockaddr *sin, socklen_t len)
{
#ifdef NO_IPV6
        static char ip[INET_ADDRSTRLEN];
#else
        static char ip[INET6_ADDRSTRLEN];
#endif

        switch (family) {
#ifndef NO_IPV6
        case AF_INET6:
                inet_ntop(family, &((struct sockaddr_in6*)sin)->sin6_addr, ip, len);
                break;
#endif
        case AF_INET:
                inet_ntop(family, &((struct sockaddr_in*)sin)->sin_addr, ip, len);
                break;
        default:
                xsnprintf(ip, sizeof(ip), "<unknown>");
        }
        return ip;
}

#ifndef NO_IPV6

static int setup_named_sock(char *listen_addr, int listen_port, struct socketlist *socklist)
{
        int socknum = 0;
        char pbuf[NI_MAXSERV];
        struct addrinfo hints, *ai0, *ai;
        int gai;
        long flags;

        xsnprintf(pbuf, sizeof(pbuf), "%d", listen_port);
        memset(&hints, 0, sizeof(hints));
        hints.ai_family = AF_UNSPEC;
        hints.ai_socktype = SOCK_STREAM;
        hints.ai_protocol = IPPROTO_TCP;
        hints.ai_flags = AI_PASSIVE;

        gai = getaddrinfo(listen_addr, pbuf, &hints, &ai0);
        if (gai) {
                logerror("getaddrinfo() for %s failed: %s", listen_addr, gai_strerror(gai));
                return 0;
        }

        for (ai = ai0; ai; ai = ai->ai_next) {
                int sockfd;

                sockfd = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
                if (sockfd < 0)
                        continue;
                if (sockfd >= FD_SETSIZE) {
                        logerror("Socket descriptor too large");
                        close(sockfd);
                        continue;
                }

#ifdef IPV6_V6ONLY
                if (ai->ai_family == AF_INET6) {
                        int on = 1;
                        setsockopt(sockfd, IPPROTO_IPV6, IPV6_V6ONLY,
                                   &on, sizeof(on));
                        /* Note: error is not fatal */
                }
#endif

                if (set_reuse_addr(sockfd)) {
                        logerror("Could not set SO_REUSEADDR: %s", strerror(errno));
                        close(sockfd);
                        continue;
                }

                set_keep_alive(sockfd);

                if (bind(sockfd, ai->ai_addr, ai->ai_addrlen) < 0) {
                        logerror("Could not bind to %s: %s",
                                 ip2str(ai->ai_family, ai->ai_addr, ai->ai_addrlen),
                                 strerror(errno));
                        close(sockfd);
                        continue;       /* not fatal */
                }
                if (listen(sockfd, 5) < 0) {
                        logerror("Could not listen to %s: %s",
                                 ip2str(ai->ai_family, ai->ai_addr, ai->ai_addrlen),
                                 strerror(errno));
                        close(sockfd);
                        continue;       /* not fatal */
                }

                flags = fcntl(sockfd, F_GETFD, 0);
                if (flags >= 0)
                        fcntl(sockfd, F_SETFD, flags | FD_CLOEXEC);

                ALLOC_GROW(socklist->list, socklist->nr + 1, socklist->alloc);
                socklist->list[socklist->nr++] = sockfd;
                socknum++;
        }

        freeaddrinfo(ai0);

        return socknum;
}

#else /* NO_IPV6 */

static int setup_named_sock(char *listen_addr, int listen_port, struct socketlist *socklist)
{
        struct sockaddr_in sin;
        int sockfd;
        long flags;

        memset(&sin, 0, sizeof sin);
        sin.sin_family = AF_INET;
        sin.sin_port = htons(listen_port);

        if (listen_addr) {
                /* Well, host better be an IP address here. */
                if (inet_pton(AF_INET, listen_addr, &sin.sin_addr.s_addr) <= 0)
                        return 0;
        } else {
                sin.sin_addr.s_addr = htonl(INADDR_ANY);
        }

        sockfd = socket(AF_INET, SOCK_STREAM, 0);
        if (sockfd < 0)
                return 0;

        if (set_reuse_addr(sockfd)) {
                logerror("Could not set SO_REUSEADDR: %s", strerror(errno));
                close(sockfd);
                return 0;
        }

        set_keep_alive(sockfd);

        if ( bind(sockfd, (struct sockaddr *)&sin, sizeof sin) < 0 ) {
                logerror("Could not bind to %s: %s",
                         ip2str(AF_INET, (struct sockaddr *)&sin, sizeof(sin)),
                         strerror(errno));
                close(sockfd);
                return 0;
        }

        if (listen(sockfd, 5) < 0) {
                logerror("Could not listen to %s: %s",
                         ip2str(AF_INET, (struct sockaddr *)&sin, sizeof(sin)),
                         strerror(errno));
                close(sockfd);
                return 0;
        }

        flags = fcntl(sockfd, F_GETFD, 0);
        if (flags >= 0)
                fcntl(sockfd, F_SETFD, flags | FD_CLOEXEC);

        ALLOC_GROW(socklist->list, socklist->nr + 1, socklist->alloc);
        socklist->list[socklist->nr++] = sockfd;
        return 1;
}

#endif

static void socksetup(struct string_list *listen_addr, int listen_port, struct socketlist *socklist)
{
        if (!listen_addr->nr)
                setup_named_sock(NULL, listen_port, socklist);
        else {
                int i, socknum;
                for (i = 0; i < listen_addr->nr; i++) {
                        socknum = setup_named_sock(listen_addr->items[i].string,
                                                   listen_port, socklist);

                        if (socknum == 0)
                                logerror("unable to allocate any listen sockets for host %s on port %u",
                                         listen_addr->items[i].string, listen_port);
                }
        }
}

static int service_loop(struct socketlist *socklist)
{
        struct pollfd *pfd;
        int i;

        pfd = xcalloc(socklist->nr, sizeof(struct pollfd));

        for (i = 0; i < socklist->nr; i++) {
                pfd[i].fd = socklist->list[i];
                pfd[i].events = POLLIN;
        }

        signal(SIGCHLD, child_handler);

        for (;;) {
                int i;

                check_dead_children();

                if (poll(pfd, socklist->nr, -1) < 0) {
                        if (errno != EINTR) {
                                logerror("Poll failed, resuming: %s",
                                      strerror(errno));
                                sleep(1);
                        }
                        continue;
                }

                for (i = 0; i < socklist->nr; i++) {
                        if (pfd[i].revents & POLLIN) {
                                union {
                                        struct sockaddr sa;
                                        struct sockaddr_in sai;
#ifndef NO_IPV6
                                        struct sockaddr_in6 sai6;
#endif
                                } ss;
                                socklen_t sslen = sizeof(ss);
                                int incoming = accept(pfd[i].fd, &ss.sa, &sslen);
                                if (incoming < 0) {
                                        switch (errno) {
                                        case EAGAIN:
                                        case EINTR:
                                        case ECONNABORTED:
                                                continue;
                                        default:
                                                die_errno("accept returned");
                                        }
                                }
                                handle(incoming, &ss.sa, sslen);
                        }
                }
        }
}

#ifdef NO_POSIX_GOODIES

struct credentials;

static void drop_privileges(struct credentials *cred)
{
        /* nothing */
}

static struct credentials *prepare_credentials(const char *user_name,
    const char *group_name)
{
        die("--user not supported on this platform");
}

#else

struct credentials {
        struct passwd *pass;
        gid_t gid;
};

static void drop_privileges(struct credentials *cred)
{
        if (cred && (initgroups(cred->pass->pw_name, cred->gid) ||
            setgid (cred->gid) || setuid(cred->pass->pw_uid)))
                die("cannot drop privileges");
}

static struct credentials *prepare_credentials(const char *user_name,
    const char *group_name)
{
        static struct credentials c;

        c.pass = getpwnam(user_name);
        if (!c.pass)
                die("user not found - %s", user_name);

        if (!group_name)
                c.gid = c.pass->pw_gid;
        else {
                struct group *group = getgrnam(group_name);
                if (!group)
                        die("group not found - %s", group_name);

                c.gid = group->gr_gid;
        }

        return &c;
}
#endif

static int serve(struct string_list *listen_addr, int listen_port,
    struct credentials *cred)
{
        struct socketlist socklist = { NULL, 0, 0 };

        socksetup(listen_addr, listen_port, &socklist);
        if (socklist.nr == 0)
                die("unable to allocate any listen sockets on port %u",
                    listen_port);

        drop_privileges(cred);

        loginfo("Ready to rumble");

        return service_loop(&socklist);
}

int main(int argc, char **argv)
{
        int listen_port = 0;
        struct string_list listen_addr = STRING_LIST_INIT_NODUP;
        int serve_mode = 0, inetd_mode = 0;
        const char *pid_file = NULL, *user_name = NULL, *group_name = NULL;
        int detach = 0;
        struct credentials *cred = NULL;
        int i;

        git_setup_gettext();

        git_extract_argv0_path(argv[0]);

        for (i = 1; i < argc; i++) {
                char *arg = argv[i];
                const char *v;

                if (skip_prefix(arg, "--listen=", &v)) {
                        string_list_append(&listen_addr, xstrdup_tolower(v));
                        continue;
                }
                if (skip_prefix(arg, "--port=", &v)) {
                        char *end;
                        unsigned long n;
                        n = strtoul(v, &end, 0);
                        if (*v && !*end) {
                                listen_port = n;
                                continue;
                        }
                }
                if (!strcmp(arg, "--serve")) {
                        serve_mode = 1;
                        continue;
                }
                if (!strcmp(arg, "--inetd")) {
                        inetd_mode = 1;
                        log_syslog = 1;
                        continue;
                }
                if (!strcmp(arg, "--verbose")) {
                        verbose = 1;
                        continue;
                }
                if (!strcmp(arg, "--syslog")) {
                        log_syslog = 1;
                        continue;
                }
                if (!strcmp(arg, "--export-all")) {
                        export_all_trees = 1;
                        continue;
                }
                if (skip_prefix(arg, "--access-hook=", &v)) {
                        access_hook = v;
                        continue;
                }
                if (skip_prefix(arg, "--timeout=", &v)) {
                        timeout = atoi(v);
                        continue;
                }
                if (skip_prefix(arg, "--init-timeout=", &v)) {
                        init_timeout = atoi(v);
                        continue;
                }
                if (skip_prefix(arg, "--max-connections=", &v)) {
                        max_connections = atoi(v);
                        if (max_connections < 0)
                                max_connections = 0;            /* unlimited */
                        continue;
                }
                if (!strcmp(arg, "--strict-paths")) {
                        strict_paths = 1;
                        continue;
                }
                if (skip_prefix(arg, "--base-path=", &v)) {
                        base_path = v;
                        continue;
                }
                if (!strcmp(arg, "--base-path-relaxed")) {
                        base_path_relaxed = 1;
                        continue;
                }
                if (skip_prefix(arg, "--interpolated-path=", &v)) {
                        interpolated_path = v;
                        continue;
                }
                if (!strcmp(arg, "--reuseaddr")) {
                        reuseaddr = 1;
                        continue;
                }
                if (!strcmp(arg, "--user-path")) {
                        user_path = "";
                        continue;
                }
                if (skip_prefix(arg, "--user-path=", &v)) {
                        user_path = v;
                        continue;
                }
                if (skip_prefix(arg, "--pid-file=", &v)) {
                        pid_file = v;
                        continue;
                }
                if (!strcmp(arg, "--detach")) {
                        detach = 1;
                        log_syslog = 1;
                        continue;
                }
                if (skip_prefix(arg, "--user=", &v)) {
                        user_name = v;
                        continue;
                }
                if (skip_prefix(arg, "--group=", &v)) {
                        group_name = v;
                        continue;
                }
                if (skip_prefix(arg, "--enable=", &v)) {
                        enable_service(v, 1);
                        continue;
                }
                if (skip_prefix(arg, "--disable=", &v)) {
                        enable_service(v, 0);
                        continue;
                }
                if (skip_prefix(arg, "--allow-override=", &v)) {
                        make_service_overridable(v, 1);
                        continue;
                }
                if (skip_prefix(arg, "--forbid-override=", &v)) {
                        make_service_overridable(v, 0);
                        continue;
                }
                if (!strcmp(arg, "--informative-errors")) {
                        informative_errors = 1;
                        continue;
                }
                if (!strcmp(arg, "--no-informative-errors")) {
                        informative_errors = 0;
                        continue;
                }
                if (!strcmp(arg, "--")) {
                        ok_paths = &argv[i+1];
                        break;
                } else if (arg[0] != '-') {
                        ok_paths = &argv[i];
                        break;
                }

                usage(daemon_usage);
        }

        if (log_syslog) {
                openlog("git-daemon", LOG_PID, LOG_DAEMON);
                set_die_routine(daemon_die);
        } else
                /* avoid splitting a message in the middle */
                setvbuf(stderr, NULL, _IOFBF, 4096);

        if (inetd_mode && (detach || group_name || user_name))
                die("--detach, --user and --group are incompatible with --inetd");

        if (inetd_mode && (listen_port || (listen_addr.nr > 0)))
                die("--listen= and --port= are incompatible with --inetd");
        else if (listen_port == 0)
                listen_port = DEFAULT_GIT_PORT;

        if (group_name && !user_name)
                die("--group supplied without --user");

        if (user_name)
                cred = prepare_credentials(user_name, group_name);

        if (strict_paths && (!ok_paths || !*ok_paths))
                die("option --strict-paths requires a whitelist");

        if (base_path && !is_directory(base_path))
                die("base-path '%s' does not exist or is not a directory",
                    base_path);

        if (inetd_mode) {
                if (!freopen("/dev/null", "w", stderr))
                        die_errno("failed to redirect stderr to /dev/null");
        }

        if (inetd_mode || serve_mode)
                return execute();

        if (detach) {
                if (daemonize())
                        die("--detach not supported on this platform");
        } else
                sanitize_stdfds();

        if (pid_file)
                write_file(pid_file, "%"PRIuMAX, (uintmax_t) getpid());

        /* prepare argv for serving-processes */
        argv_array_push(&cld_argv, argv[0]); /* git-daemon */
        argv_array_push(&cld_argv, "--serve");
        for (i = 1; i < argc; ++i)
                argv_array_push(&cld_argv, argv[i]);

        return serve(&listen_addr, listen_port, cred);
}