contrib/chg/chg.c

chg: detect chg started by chg

Sometimes people may create a symbol link from hg to chg, or write a wrapper
script named hg calling chg. Without $HG and $CHGHG set, this will lead to
chg executes itself causing deadlock. The user will notice chg hangs for some
time and aborts with a timed out message, without knowing the root cause and
how to solve it.

This patch sets a dummy environment variable before executing hg to detect
this situation, and print a fatal message with some possible solutions.

CHGINTERNALMARK is set by chg client to detect the situation that chg is
started by chg. It is temporary and should be dropped to avoid possible
side effects.

/*
 * A fast client for Mercurial command server
 *
 * Copyright (c) 2011 Yuya Nishihara <[e-mail]>
 *
 * This software may be used and distributed according to the terms of the
 * GNU General Public License version 2 or any later version.
 */

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/un.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>

#include "hgclient.h"
#include "util.h"

#ifndef UNIX_PATH_MAX
#define UNIX_PATH_MAX (sizeof(((struct sockaddr_un *)NULL)->sun_path))
#endif

struct cmdserveropts {
	char sockname[UNIX_PATH_MAX];
	char lockfile[UNIX_PATH_MAX];
	char pidfile[UNIX_PATH_MAX];
	size_t argsize;
	const char **args;
	int lockfd;
};

static void initcmdserveropts(struct cmdserveropts *opts) {
	memset(opts, 0, sizeof(struct cmdserveropts));
	opts->lockfd = -1;
}

static void freecmdserveropts(struct cmdserveropts *opts) {
	free(opts->args);
	opts->args = NULL;
	opts->argsize = 0;
}

/*
 * Test if an argument is a sensitive flag that should be passed to the server.
 * Return 0 if not, otherwise the number of arguments starting from the current
 * one that should be passed to the server.
 */
static size_t testsensitiveflag(const char *arg)
{
	static const struct {
		const char *name;
		size_t narg;
	} flags[] = {
		{"--config", 1},
		{"--cwd", 1},
		{"--repo", 1},
		{"--repository", 1},
		{"--traceback", 0},
		{"-R", 1},
	};
	size_t i;
	for (i = 0; i < sizeof(flags) / sizeof(flags[0]); ++i) {
		size_t len = strlen(flags[i].name);
		size_t narg = flags[i].narg;
		if (memcmp(arg, flags[i].name, len) == 0) {
			if (arg[len] == '\0') {  /* --flag (value) */
				return narg + 1;
			} else if (arg[len] == '=' && narg > 0) {  /* --flag=value */
				return 1;
			} else if (flags[i].name[1] != '-') {  /* short flag */
				return 1;
			}
		}
	}
	return 0;
}

/*
 * Parse argv[] and put sensitive flags to opts->args
 */
static void setcmdserverargs(struct cmdserveropts *opts,
			     int argc, const char *argv[])
{
	size_t i, step;
	opts->argsize = 0;
	for (i = 0, step = 1; i < (size_t)argc; i += step, step = 1) {
		if (!argv[i])
			continue;  /* pass clang-analyse */
		if (strcmp(argv[i], "--") == 0)
			break;
		size_t n = testsensitiveflag(argv[i]);
		if (n == 0 || i + n > (size_t)argc)
			continue;
		opts->args = reallocx(opts->args,
				      (n + opts->argsize) * sizeof(char *));
		memcpy(opts->args + opts->argsize, argv + i,
		       sizeof(char *) * n);
		opts->argsize += n;
		step = n;
	}
}

static void preparesockdir(const char *sockdir)
{
	int r;
	r = mkdir(sockdir, 0700);
	if (r < 0 && errno != EEXIST)
		abortmsg("cannot create sockdir %s (errno = %d)",
			 sockdir, errno);

	struct stat st;
	r = lstat(sockdir, &st);
	if (r < 0)
		abortmsg("cannot stat %s (errno = %d)", sockdir, errno);
	if (!S_ISDIR(st.st_mode))
		abortmsg("cannot create sockdir %s (file exists)", sockdir);
	if (st.st_uid != geteuid() || st.st_mode & 0077)
		abortmsg("insecure sockdir %s", sockdir);
}

static void setcmdserveropts(struct cmdserveropts *opts)
{
	int r;
	char sockdir[UNIX_PATH_MAX];
	const char *envsockname = getenv("CHGSOCKNAME");
	if (!envsockname) {
		/* by default, put socket file in secure directory
		 * (permission of socket file may be ignored on some Unices) */
		const char *tmpdir = getenv("TMPDIR");
		if (!tmpdir)
			tmpdir = "/tmp";
		r = snprintf(sockdir, sizeof(sockdir), "%s/chg%d",
			     tmpdir, geteuid());
		if (r < 0 || (size_t)r >= sizeof(sockdir))
			abortmsg("too long TMPDIR (r = %d)", r);
		preparesockdir(sockdir);
	}

	const char *basename = (envsockname) ? envsockname : sockdir;
	const char *sockfmt = (envsockname) ? "%s" : "%s/server";
	const char *lockfmt = (envsockname) ? "%s.lock" : "%s/lock";
	const char *pidfmt = (envsockname) ? "%s.pid" : "%s/pid";
	r = snprintf(opts->sockname, sizeof(opts->sockname), sockfmt, basename);
	if (r < 0 || (size_t)r >= sizeof(opts->sockname))
		abortmsg("too long TMPDIR or CHGSOCKNAME (r = %d)", r);
	r = snprintf(opts->lockfile, sizeof(opts->lockfile), lockfmt, basename);
	if (r < 0 || (size_t)r >= sizeof(opts->lockfile))
		abortmsg("too long TMPDIR or CHGSOCKNAME (r = %d)", r);
	r = snprintf(opts->pidfile, sizeof(opts->pidfile), pidfmt, basename);
	if (r < 0 || (size_t)r >= sizeof(opts->pidfile))
		abortmsg("too long TMPDIR or CHGSOCKNAME (r = %d)", r);
}

/*
 * Acquire a file lock that indicates a client is trying to start and connect
 * to a server, before executing a command. The lock is released upon exit or
 * explicit unlock. Will block if the lock is held by another process.
 */
static void lockcmdserver(struct cmdserveropts *opts)
{
	if (opts->lockfd == -1) {
		opts->lockfd = open(opts->lockfile, O_RDWR | O_CREAT | O_NOFOLLOW, 0600);
		if (opts->lockfd == -1)
			abortmsg("cannot create lock file %s", opts->lockfile);
	}
	int r = flock(opts->lockfd, LOCK_EX);
	if (r == -1)
		abortmsg("cannot acquire lock");
}

/*
 * Release the file lock held by calling lockcmdserver. Will do nothing if
 * lockcmdserver is not called.
 */
static void unlockcmdserver(struct cmdserveropts *opts)
{
	if (opts->lockfd == -1)
		return;
	flock(opts->lockfd, LOCK_UN);
	close(opts->lockfd);
	opts->lockfd = -1;
}

static const char *gethgcmd(void)
{
	static const char *hgcmd = NULL;
	if (!hgcmd) {
		hgcmd = getenv("CHGHG");
		if (!hgcmd || hgcmd[0] == '\0')
			hgcmd = getenv("HG");
		if (!hgcmd || hgcmd[0] == '\0')
			hgcmd = "hg";
	}
	return hgcmd;
}

static void execcmdserver(const struct cmdserveropts *opts)
{
	const char *hgcmd = gethgcmd();

	const char *baseargv[] = {
		hgcmd,
		"serve",
		"--cwd", "/",
		"--cmdserver", "chgunix",
		"--address", opts->sockname,
		"--daemon-postexec", "none",
		"--pid-file", opts->pidfile,
		"--config", "extensions.chgserver=",
		/* wrap root ui so that it can be disabled/enabled by config */
		"--config", "progress.assume-tty=1",
	};
	size_t baseargvsize = sizeof(baseargv) / sizeof(baseargv[0]);
	size_t argsize = baseargvsize + opts->argsize + 1;

	const char **argv = mallocx(sizeof(char *) * argsize);
	memcpy(argv, baseargv, sizeof(baseargv));
	memcpy(argv + baseargvsize, opts->args, sizeof(char *) * opts->argsize);
	argv[argsize - 1] = NULL;

	if (putenv("CHGINTERNALMARK=") != 0)
		abortmsg("failed to putenv (errno = %d)", errno);
	if (execvp(hgcmd, (char **)argv) < 0)
		abortmsg("failed to exec cmdserver (errno = %d)", errno);
	free(argv);
}

/* Retry until we can connect to the server. Give up after some time. */
static hgclient_t *retryconnectcmdserver(struct cmdserveropts *opts, pid_t pid)
{
	static const struct timespec sleepreq = {0, 10 * 1000000};
	int pst = 0;

	for (unsigned int i = 0; i < 10 * 100; i++) {
		hgclient_t *hgc = hgc_open(opts->sockname);
		if (hgc)
			return hgc;

		if (pid > 0) {
			/* collect zombie if child process fails to start */
			int r = waitpid(pid, &pst, WNOHANG);
			if (r != 0)
				goto cleanup;
		}

		nanosleep(&sleepreq, NULL);
	}

	abortmsg("timed out waiting for cmdserver %s", opts->sockname);
	return NULL;

cleanup:
	if (WIFEXITED(pst)) {
		abortmsg("cmdserver exited with status %d", WEXITSTATUS(pst));
	} else if (WIFSIGNALED(pst)) {
		abortmsg("cmdserver killed by signal %d", WTERMSIG(pst));
	} else {
		abortmsg("error white waiting cmdserver");
	}
	return NULL;
}

/* Connect to a cmdserver. Will start a new server on demand. */
static hgclient_t *connectcmdserver(struct cmdserveropts *opts)
{
	hgclient_t *hgc = hgc_open(opts->sockname);
	if (hgc)
		return hgc;

	lockcmdserver(opts);
	hgc = hgc_open(opts->sockname);
	if (hgc) {
		unlockcmdserver(opts);
		debugmsg("cmdserver is started by another process");
		return hgc;
	}

	debugmsg("start cmdserver at %s", opts->sockname);

	pid_t pid = fork();
	if (pid < 0)
		abortmsg("failed to fork cmdserver process");
	if (pid == 0) {
		/* do not leak lockfd to hg */
		close(opts->lockfd);
		/* bypass uisetup() of pager extension */
		int nullfd = open("/dev/null", O_WRONLY);
		if (nullfd >= 0) {
			dup2(nullfd, fileno(stdout));
			close(nullfd);
		}
		execcmdserver(opts);
	} else {
		hgc = retryconnectcmdserver(opts, pid);
	}

	unlockcmdserver(opts);
	return hgc;
}

static void killcmdserver(const struct cmdserveropts *opts, int sig)
{
	FILE *fp = fopen(opts->pidfile, "r");
	if (!fp)
		abortmsg("cannot open %s (errno = %d)", opts->pidfile, errno);
	int pid = 0;
	int n = fscanf(fp, "%d", &pid);
	fclose(fp);
	if (n != 1 || pid <= 0)
		abortmsg("cannot read pid from %s", opts->pidfile);

	if (kill((pid_t)pid, sig) < 0) {
		if (errno == ESRCH)
			return;
		abortmsg("cannot kill %d (errno = %d)", pid, errno);
	}
}

static pid_t peerpid = 0;

static void forwardsignal(int sig)
{
	assert(peerpid > 0);
	if (kill(peerpid, sig) < 0)
		abortmsg("cannot kill %d (errno = %d)", peerpid, errno);
	debugmsg("forward signal %d", sig);
}

static void handlestopsignal(int sig)
{
	sigset_t unblockset, oldset;
	struct sigaction sa, oldsa;
	if (sigemptyset(&unblockset) < 0)
		goto error;
	if (sigaddset(&unblockset, sig) < 0)
		goto error;
	memset(&sa, 0, sizeof(sa));
	sa.sa_handler = SIG_DFL;
	sa.sa_flags = SA_RESTART;
	if (sigemptyset(&sa.sa_mask) < 0)
		goto error;

	forwardsignal(sig);
	if (raise(sig) < 0)  /* resend to self */
		goto error;
	if (sigaction(sig, &sa, &oldsa) < 0)
		goto error;
	if (sigprocmask(SIG_UNBLOCK, &unblockset, &oldset) < 0)
		goto error;
	/* resent signal will be handled before sigprocmask() returns */
	if (sigprocmask(SIG_SETMASK, &oldset, NULL) < 0)
		goto error;
	if (sigaction(sig, &oldsa, NULL) < 0)
		goto error;
	return;

error:
	abortmsg("failed to handle stop signal (errno = %d)", errno);
}

static void setupsignalhandler(pid_t pid)
{
	if (pid <= 0)
		return;
	peerpid = pid;

	struct sigaction sa;
	memset(&sa, 0, sizeof(sa));
	sa.sa_handler = forwardsignal;
	sa.sa_flags = SA_RESTART;
	if (sigemptyset(&sa.sa_mask) < 0)
		goto error;

	if (sigaction(SIGHUP, &sa, NULL) < 0)
		goto error;
	if (sigaction(SIGINT, &sa, NULL) < 0)
		goto error;

	/* terminate frontend by double SIGTERM in case of server freeze */
	sa.sa_flags |= SA_RESETHAND;
	if (sigaction(SIGTERM, &sa, NULL) < 0)
		goto error;

	/* propagate job control requests to worker */
	sa.sa_handler = forwardsignal;
	sa.sa_flags = SA_RESTART;
	if (sigaction(SIGCONT, &sa, NULL) < 0)
		goto error;
	sa.sa_handler = handlestopsignal;
	sa.sa_flags = SA_RESTART;
	if (sigaction(SIGTSTP, &sa, NULL) < 0)
		goto error;

	return;

error:
	abortmsg("failed to set up signal handlers (errno = %d)", errno);
}

/* This implementation is based on hgext/pager.py (pre 369741ef7253) */
static void setuppager(hgclient_t *hgc, const char *const args[],
		       size_t argsize)
{
	const char *pagercmd = hgc_getpager(hgc, args, argsize);
	if (!pagercmd)
		return;

	int pipefds[2];
	if (pipe(pipefds) < 0)
		return;
	pid_t pid = fork();
	if (pid < 0)
		goto error;
	if (pid == 0) {
		close(pipefds[0]);
		if (dup2(pipefds[1], fileno(stdout)) < 0)
			goto error;
		if (isatty(fileno(stderr))) {
			if (dup2(pipefds[1], fileno(stderr)) < 0)
				goto error;
		}
		close(pipefds[1]);
		hgc_attachio(hgc);  /* reattach to pager */
		return;
	} else {
		dup2(pipefds[0], fileno(stdin));
		close(pipefds[0]);
		close(pipefds[1]);

		int r = execlp("/bin/sh", "/bin/sh", "-c", pagercmd, NULL);
		if (r < 0) {
			abortmsg("cannot start pager '%s' (errno = %d)",
				 pagercmd, errno);
		}
		return;
	}

error:
	close(pipefds[0]);
	close(pipefds[1]);
	abortmsg("failed to prepare pager (errno = %d)", errno);
}

/*
 * Test whether the command is unsupported or not. This is not designed to
 * cover all cases. But it's fast, does not depend on the server and does
 * not return false positives.
 */
static int isunsupported(int argc, const char *argv[])
{
	enum {
		SERVE = 1,
		DAEMON = 2,
		SERVEDAEMON = SERVE | DAEMON,
		TIME = 4,
	};
	unsigned int state = 0;
	int i;
	for (i = 0; i < argc; ++i) {
		if (strcmp(argv[i], "--") == 0)
			break;
		if (i == 0 && strcmp("serve", argv[i]) == 0)
			state |= SERVE;
		else if (strcmp("-d", argv[i]) == 0 ||
			 strcmp("--daemon", argv[i]) == 0)
			state |= DAEMON;
		else if (strcmp("--time", argv[i]) == 0)
			state |= TIME;
	}
	return (state & TIME) == TIME ||
	       (state & SERVEDAEMON) == SERVEDAEMON;
}

static void execoriginalhg(const char *argv[])
{
	debugmsg("execute original hg");
	if (execvp(gethgcmd(), (char **)argv) < 0)
		abortmsg("failed to exec original hg (errno = %d)", errno);
}

int main(int argc, const char *argv[], const char *envp[])
{
	if (getenv("CHGDEBUG"))
		enabledebugmsg();

	if (getenv("CHGINTERNALMARK"))
		abortmsg("chg started by chg detected.\n"
			 "Please make sure ${HG:-hg} is not a symlink or "
			 "wrapper to chg. Alternatively, set $CHGHG to the "
			 "path of real hg.");

	if (isunsupported(argc - 1, argv + 1))
		execoriginalhg(argv);

	struct cmdserveropts opts;
	initcmdserveropts(&opts);
	setcmdserveropts(&opts);
	setcmdserverargs(&opts, argc, argv);

	if (argc == 2) {
		int sig = 0;
		if (strcmp(argv[1], "--kill-chg-daemon") == 0)
			sig = SIGTERM;
		if (strcmp(argv[1], "--reload-chg-daemon") == 0)
			sig = SIGHUP;
		if (sig > 0) {
			killcmdserver(&opts, sig);
			return 0;
		}
	}

	hgclient_t *hgc = connectcmdserver(&opts);
	if (!hgc)
		abortmsg("cannot open hg client");

	setupsignalhandler(hgc_peerpid(hgc));
	hgc_setenv(hgc, envp);
	setuppager(hgc, argv + 1, argc - 1);
	int exitcode = hgc_runcommand(hgc, argv + 1, argc - 1);
	hgc_close(hgc);
	freecmdserveropts(&opts);
	return exitcode;
}