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#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"

static int log_syslog;
static int verbose;

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] [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;

/* 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)
{
char *path;

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

if (base_path) {
static char rpath[PATH_MAX];
if (*dir != '/') {
/* Forbid possible base-path evasion using ~paths. */
logerror("'%s': Non-absolute path denied (base-path active)");
return NULL;
}
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 */
execlp("git-upload-pack", "git-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;
}
}

#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 (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 ( 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, "--")) {
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);
}
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