documentation: add brief mention of cat-file to tutorial part I

[git/debian.git] / daemon.c

#include <signal.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/poll.h>
#include <netdb.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <syslog.h>
#include "pkt-line.h"
#include "cache.h"
#include "exec_cmd.h"

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

static const char daemon_usage[] =
"git-daemon [--verbose] [--syslog] [--inetd | --port=n] [--export-all]\n"
"           [--timeout=n] [--init-timeout=n] [--strict-paths]\n"
"           [--base-path=path] [--user-path | --user-path=path]\n"
"           [--reuseaddr] [directory...]";

/* List of acceptable pathname prefixes */
static char **ok_paths = NULL;
static int strict_paths = 0;

/* If this is set, git-daemon-export-ok is not required */
static int export_all_trees = 0;

/* Take all paths relative to this one if non-NULL */
static char *base_path = NULL;

/* 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 char *user_path = NULL;

/* Timeout, and initial timeout */
static unsigned int timeout = 0;
static unsigned int init_timeout = 0;

static void logreport(int priority, const char *err, va_list params)
{
        /* We should do a single write so that it is atomic and output
         * of several processes do not get intermingled. */
        char buf[1024];
        int buflen;
        int maxlen, msglen;

        /* sizeof(buf) should be big enough for "[pid] \n" */
        buflen = snprintf(buf, sizeof(buf), "[%ld] ", (long) getpid());

        maxlen = sizeof(buf) - buflen - 1; /* -1 for our own LF */
        msglen = vsnprintf(buf + buflen, maxlen, err, params);

        if (log_syslog) {
                syslog(priority, "%s", buf);
                return;
        }

        /* maxlen counted our own LF but also counts space given to
         * vsnprintf for the terminating NUL.  We want to make sure that
         * we have space for our own LF and NUL after the "meat" of the
         * message, so truncate it at maxlen - 1.
         */
        if (msglen > maxlen - 1)
                msglen = maxlen - 1;
        else if (msglen < 0)
                msglen = 0; /* Protect against weird return values. */
        buflen += msglen;

        buf[buflen++] = '\n';
        buf[buflen] = '\0';

        write(2, buf, buflen);
}

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

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 int avoid_alias(char *p)
{
        int sl, ndot;

        /* 
         * This resurrects the belts and suspenders paranoia check by HPA
         * done in <435560F7.4080006@zytor.com> thread, now enter_repo()
         * does not do getcwd() based path canonicalizations.
         *
         * sl becomes true immediately after seeing '/' and continues to
         * be true as long as dots continue after that without intervening
         * non-dot character.
         */
        if (!p || (*p != '/' && *p != '~'))
                return -1;
        sl = 1; ndot = 0;
        p++;

        while (1) {
                char ch = *p++;
                if (sl) {
                        if (ch == '.')
                                ndot++;
                        else if (ch == '/') {
                                if (ndot < 3)
                                        /* reject //, /./ and /../ */
                                        return -1;
                                ndot = 0;
                        }
                        else if (ch == 0) {
                                if (0 < ndot && ndot < 3)
                                        /* reject /.$ and /..$ */
                                        return -1;
                                return 0;
                        }
                        else
                                sl = ndot = 0;
                }
                else if (ch == 0)
                        return 0;
                else if (ch == '/') {
                        sl = 1;
                        ndot = 0;
                }
        }
}

static char *path_ok(char *dir)
{
        static char rpath[PATH_MAX];
        char *path;

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

        path = enter_repo(dir, strict_paths);

        if (!path) {
                logerror("'%s': unable to chdir or not a git archive", 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 */
}

static int upload(char *dir)
{
        /* Timeout as string */
        char timeout_buf[64];
        const char *path;

        loginfo("Request for '%s'", dir);

        if (!(path = path_ok(dir)))
                return -1;

        /*
         * 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 -1;
        }

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

        snprintf(timeout_buf, sizeof timeout_buf, "--timeout=%u", timeout);

        /* git-upload-pack only ever reads stuff, so this is safe */
        execl_git_cmd("upload-pack", "--strict", timeout_buf, ".", NULL);
        return -1;
}

static int execute(void)
{
        static char line[1000];
        int len;

        alarm(init_timeout ? init_timeout : timeout);
        len = packet_read_line(0, line, sizeof(line));
        alarm(0);

        if (len && line[len-1] == '\n')
                line[--len] = 0;

        if (!strncmp("git-upload-pack ", line, 16))
                return upload(line+16);

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


/*
 * We count spawned/reaped separately, just to avoid any
 * races when updating them from signals. The SIGCHLD handler
 * will only update children_reaped, and the fork logic will
 * only update children_spawned.
 *
 * MAX_CHILDREN should be a power-of-two to make the modulus
 * operation cheap. It should also be at least twice
 * the maximum number of connections we will ever allow.
 */
#define MAX_CHILDREN 128

static int max_connections = 25;

/* These are updated by the signal handler */
static volatile unsigned int children_reaped = 0;
static pid_t dead_child[MAX_CHILDREN];

/* These are updated by the main loop */
static unsigned int children_spawned = 0;
static unsigned int children_deleted = 0;

static struct child {
        pid_t pid;
        int addrlen;
        struct sockaddr_storage address;
} live_child[MAX_CHILDREN];

static void add_child(int idx, pid_t pid, struct sockaddr *addr, int addrlen)
{
        live_child[idx].pid = pid;
        live_child[idx].addrlen = addrlen;
        memcpy(&live_child[idx].address, addr, addrlen);
}

/*
 * Walk from "deleted" to "spawned", and remove child "pid".
 *
 * We move everything up by one, since the new "deleted" will
 * be one higher.
 */
static void remove_child(pid_t pid, unsigned deleted, unsigned spawned)
{
        struct child n;

        deleted %= MAX_CHILDREN;
        spawned %= MAX_CHILDREN;
        if (live_child[deleted].pid == pid) {
                live_child[deleted].pid = -1;
                return;
        }
        n = live_child[deleted];
        for (;;) {
                struct child m;
                deleted = (deleted + 1) % MAX_CHILDREN;
                if (deleted == spawned)
                        die("could not find dead child %d\n", pid);
                m = live_child[deleted];
                live_child[deleted] = n;
                if (m.pid == pid)
                        return;
                n = m;
        }
}

/*
 * This gets called if the number of connections grows
 * past "max_connections".
 *
 * We _should_ start off by searching for connections
 * from the same IP, and if there is some address wth
 * multiple connections, we should kill that first.
 *
 * As it is, we just "randomly" kill 25% of the connections,
 * and our pseudo-random generator sucks too. I have no
 * shame.
 *
 * Really, this is just a place-holder for a _real_ algorithm.
 */
static void kill_some_children(int signo, unsigned start, unsigned stop)
{
        start %= MAX_CHILDREN;
        stop %= MAX_CHILDREN;
        while (start != stop) {
                if (!(start & 3))
                        kill(live_child[start].pid, signo);
                start = (start + 1) % MAX_CHILDREN;
        }
}

static void check_max_connections(void)
{
        for (;;) {
                int active;
                unsigned spawned, reaped, deleted;

                spawned = children_spawned;
                reaped = children_reaped;
                deleted = children_deleted;

                while (deleted < reaped) {
                        pid_t pid = dead_child[deleted % MAX_CHILDREN];
                        remove_child(pid, deleted, spawned);
                        deleted++;
                }
                children_deleted = deleted;

                active = spawned - deleted;
                if (active <= max_connections)
                        break;

                /* Kill some unstarted connections with SIGTERM */
                kill_some_children(SIGTERM, deleted, spawned);
                if (active <= max_connections << 1)
                        break;

                /* If the SIGTERM thing isn't helping use SIGKILL */
                kill_some_children(SIGKILL, deleted, spawned);
                sleep(1);
        }
}

static void handle(int incoming, struct sockaddr *addr, int addrlen)
{
        pid_t pid = fork();
        char addrbuf[256] = "";
        int port = -1;

        if (pid) {
                unsigned idx;

                close(incoming);
                if (pid < 0)
                        return;

                idx = children_spawned % MAX_CHILDREN;
                children_spawned++;
                add_child(idx, pid, addr, addrlen);

                check_max_connections();
                return;
        }

        dup2(incoming, 0);
        dup2(incoming, 1);
        close(incoming);

        if (addr->sa_family == AF_INET) {
                struct sockaddr_in *sin_addr = (void *) addr;
                inet_ntop(AF_INET, &sin_addr->sin_addr, addrbuf, sizeof(addrbuf));
                port = sin_addr->sin_port;

#ifndef NO_IPV6
        } else if (addr->sa_family == AF_INET6) {
                struct sockaddr_in6 *sin6_addr = (void *) addr;

                char *buf = addrbuf;
                *buf++ = '['; *buf = '\0'; /* stpcpy() is cool */
                inet_ntop(AF_INET6, &sin6_addr->sin6_addr, buf, sizeof(addrbuf) - 1);
                strcat(buf, "]");

                port = sin6_addr->sin6_port;
#endif
        }
        loginfo("Connection from %s:%d", addrbuf, port);

        exit(execute());
}

static void child_handler(int signo)
{
        for (;;) {
                int status;
                pid_t pid = waitpid(-1, &status, WNOHANG);

                if (pid > 0) {
                        unsigned reaped = children_reaped;
                        dead_child[reaped % MAX_CHILDREN] = pid;
                        children_reaped = reaped + 1;
                        /* XXX: Custom logging, since we don't wanna getpid() */
                        if (verbose) {
                                char *dead = "";
                                if (!WIFEXITED(status) || WEXITSTATUS(status) > 0)
                                        dead = " (with error)";
                                if (log_syslog)
                                        syslog(LOG_INFO, "[%d] Disconnected%s", pid, dead);
                                else
                                        fprintf(stderr, "[%d] Disconnected%s\n", pid, dead);
                        }
                        continue;
                }
                break;
        }
}

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

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

#ifndef NO_IPV6

static int socksetup(int port, int **socklist_p)
{
        int socknum = 0, *socklist = NULL;
        int maxfd = -1;
        char pbuf[NI_MAXSERV];

        struct addrinfo hints, *ai0, *ai;
        int gai;

        sprintf(pbuf, "%d", 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(NULL, pbuf, &hints, &ai0);
        if (gai)
                die("getaddrinfo() failed: %s\n", gai_strerror(gai));

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

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

                if (bind(sockfd, ai->ai_addr, ai->ai_addrlen) < 0) {
                        close(sockfd);
                        continue;       /* not fatal */
                }
                if (listen(sockfd, 5) < 0) {
                        close(sockfd);
                        continue;       /* not fatal */
                }

                newlist = realloc(socklist, sizeof(int) * (socknum + 1));
                if (!newlist)
                        die("memory allocation failed: %s", strerror(errno));

                socklist = newlist;
                socklist[socknum++] = sockfd;

                if (maxfd < sockfd)
                        maxfd = sockfd;
        }

        freeaddrinfo(ai0);

        *socklist_p = socklist;
        return socknum;
}

#else /* NO_IPV6 */

static int socksetup(int port, int **socklist_p)
{
        struct sockaddr_in sin;
        int sockfd;

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

        memset(&sin, 0, sizeof sin);
        sin.sin_family = AF_INET;
        sin.sin_addr.s_addr = htonl(INADDR_ANY);
        sin.sin_port = htons(port);

        if (set_reuse_addr(sockfd)) {
                close(sockfd);
                return 0;
        }

        if ( bind(sockfd, (struct sockaddr *)&sin, sizeof sin) < 0 ) {
                close(sockfd);
                return 0;
        }

        if (listen(sockfd, 5) < 0) {
                close(sockfd);
                return 0;
        }

        *socklist_p = xmalloc(sizeof(int));
        **socklist_p = sockfd;
        return 1;
}

#endif

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

        pfd = xcalloc(socknum, sizeof(struct pollfd));

        for (i = 0; i < socknum; i++) {
                pfd[i].fd = socklist[i];
                pfd[i].events = POLLIN;
        }

        signal(SIGCHLD, child_handler);

        for (;;) {
                int i;

                if (poll(pfd, socknum, -1) < 0) {
                        if (errno != EINTR) {
                                error("poll failed, resuming: %s",
                                      strerror(errno));
                                sleep(1);
                        }
                        continue;
                }

                for (i = 0; i < socknum; i++) {
                        if (pfd[i].revents & POLLIN) {
                                struct sockaddr_storage ss;
                                unsigned int sslen = sizeof(ss);
                                int incoming = accept(pfd[i].fd, (struct sockaddr *)&ss, &sslen);
                                if (incoming < 0) {
                                        switch (errno) {
                                        case EAGAIN:
                                        case EINTR:
                                        case ECONNABORTED:
                                                continue;
                                        default:
                                                die("accept returned %s", strerror(errno));
                                        }
                                }
                                handle(incoming, (struct sockaddr *)&ss, sslen);
                        }
                }
        }
}

static int serve(int port)
{
        int socknum, *socklist;

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

        return service_loop(socknum, socklist);
}

int main(int argc, char **argv)
{
        int port = DEFAULT_GIT_PORT;
        int inetd_mode = 0;
        int i;

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

                if (!strncmp(arg, "--port=", 7)) {
                        char *end;
                        unsigned long n;
                        n = strtoul(arg+7, &end, 0);
                        if (arg[7] && !*end) {
                                port = n;
                                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 (!strncmp(arg, "--timeout=", 10)) {
                        timeout = atoi(arg+10);
                        continue;
                }
                if (!strncmp(arg, "--init-timeout=", 15)) {
                        init_timeout = atoi(arg+15);
                        continue;
                }
                if (!strcmp(arg, "--strict-paths")) {
                        strict_paths = 1;
                        continue;
                }
                if (!strncmp(arg, "--base-path=", 12)) {
                        base_path = arg+12;
                        continue;
                }
                if (!strcmp(arg, "--reuseaddr")) {
                        reuseaddr = 1;
                        continue;
                }
                if (!strcmp(arg, "--user-path")) {
                        user_path = "";
                        continue;
                }
                if (!strncmp(arg, "--user-path=", 12)) {
                        user_path = arg + 12;
                        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", 0, LOG_DAEMON);

        if (strict_paths && (!ok_paths || !*ok_paths)) {
                if (!inetd_mode)
                        die("git-daemon: option --strict-paths requires a whitelist");

                logerror("option --strict-paths requires a whitelist");
                exit (1);
        }

        if (inetd_mode) {
                fclose(stderr); //FIXME: workaround
                return execute();
        }

        return serve(port);
}