chg: verify XDG_RUNTIME_DIR

According to the specification [1], $XDG_RUNTIME_DIR should be ignored
unless:

  The directory MUST be owned by the user, and he MUST be the only one
  having read and write access to it. Its Unix access mode MUST be 0700.

This patch adds a check and ignores it if it does not meet part of the
criteria.

[1]: https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html

contrib/chg/chg.c

@@ -1,439 +1,457 b''
 /*
  * 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 "procutil.h"
 #include "util.h"
 
 #ifndef PATH_MAX
 #define PATH_MAX 4096
 #endif
 
 struct cmdserveropts {
 	char sockname[PATH_MAX];
 	char initsockname[PATH_MAX];
 	char redirectsockname[PATH_MAX];
 	size_t argsize;
 	const char **args;
 };
 
 static void initcmdserveropts(struct cmdserveropts *opts) {
 	memset(opts, 0, sizeof(struct cmdserveropts));
 }
 
 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)
 		abortmsgerrno("cannot create sockdir %s", sockdir);
 
 	struct stat st;
 	r = lstat(sockdir, &st);
 	if (r < 0)
 		abortmsgerrno("cannot stat %s", sockdir);
 	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);
 }
 
+/*
+ * Check if a socket directory exists and is only owned by the current user.
+ * Return 1 if so, 0 if not. This is used to check if XDG_RUNTIME_DIR can be
+ * used or not. According to the specification [1], XDG_RUNTIME_DIR should be
+ * ignored if the directory is not owned by the user with mode 0700.
+ * [1]: https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
+ */
+static int checkruntimedir(const char *sockdir)
+{
+	struct stat st;
+	int r = lstat(sockdir, &st);
+	if (r < 0) /* ex. does not exist */
+		return 0;
+	if (!S_ISDIR(st.st_mode)) /* ex. is a file, not a directory */
+		return 0;
+	return st.st_uid == geteuid() && (st.st_mode & 0777) == 0700;
+}
+
 static void getdefaultsockdir(char sockdir[], size_t size)
 {
 	/* by default, put socket file in secure directory
 	 * (${XDG_RUNTIME_DIR}/chg, or /${TMPDIR:-tmp}/chg$UID)
 	 * (permission of socket file may be ignored on some Unices) */
 	const char *runtimedir = getenv("XDG_RUNTIME_DIR");
 	int r;
-	if (runtimedir) {
+	if (runtimedir && checkruntimedir(runtimedir)) {
 		r = snprintf(sockdir, size, "%s/chg", runtimedir);
 	} else {
 		const char *tmpdir = getenv("TMPDIR");
 		if (!tmpdir)
 			tmpdir = "/tmp";
 		r = snprintf(sockdir, size, "%s/chg%d", tmpdir, geteuid());
 	}
 	if (r < 0 || (size_t)r >= size)
 		abortmsg("too long TMPDIR (r = %d)", r);
 }
 
 static void setcmdserveropts(struct cmdserveropts *opts)
 {
 	int r;
 	char sockdir[PATH_MAX];
 	const char *envsockname = getenv("CHGSOCKNAME");
 	if (!envsockname) {
 		getdefaultsockdir(sockdir, sizeof(sockdir));
 		preparesockdir(sockdir);
 	}
 
 	const char *basename = (envsockname) ? envsockname : sockdir;
 	const char *sockfmt = (envsockname) ? "%s" : "%s/server";
 	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->initsockname, sizeof(opts->initsockname),
 			"%s.%u", opts->sockname, (unsigned)getpid());
 	if (r < 0 || (size_t)r >= sizeof(opts->initsockname))
 		abortmsg("too long TMPDIR or CHGSOCKNAME (r = %d)", r);
 }
 
 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')
 #ifdef HGPATH
 			hgcmd = (HGPATH);
 #else
 			hgcmd = "hg";
 #endif
 	}
 	return hgcmd;
 }
 
 static void execcmdserver(const struct cmdserveropts *opts)
 {
 	const char *hgcmd = gethgcmd();
 
 	const char *baseargv[] = {
 		hgcmd,
 		"serve",
 		"--cmdserver", "chgunix",
 		"--address", opts->initsockname,
 		"--daemon-postexec", "chdir:/",
 	};
 	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)
 		abortmsgerrno("failed to putenv");
 	if (execvp(hgcmd, (char **)argv) < 0)
 		abortmsgerrno("failed to exec cmdserver");
 	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;
 
 	debugmsg("try connect to %s repeatedly", opts->initsockname);
 
 	unsigned int timeoutsec = 60;  /* default: 60 seconds */
 	const char *timeoutenv = getenv("CHGTIMEOUT");
 	if (timeoutenv)
 		sscanf(timeoutenv, "%u", &timeoutsec);
 
 	for (unsigned int i = 0; !timeoutsec || i < timeoutsec * 100; i++) {
 		hgclient_t *hgc = hgc_open(opts->initsockname);
 		if (hgc) {
 			debugmsg("rename %s to %s", opts->initsockname,
 					opts->sockname);
 			int r = rename(opts->initsockname, opts->sockname);
 			if (r != 0)
 				abortmsgerrno("cannot rename");
 			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->initsockname);
 	return NULL;
 
 cleanup:
 	if (WIFEXITED(pst)) {
 		if (WEXITSTATUS(pst) == 0)
 			abortmsg("could not connect to cmdserver "
 				 "(exited with status 0)");
 		debugmsg("cmdserver exited with status %d", WEXITSTATUS(pst));
 		exit(WEXITSTATUS(pst));
 	} else if (WIFSIGNALED(pst)) {
 		abortmsg("cmdserver killed by signal %d", WTERMSIG(pst));
 	} else {
 		abortmsg("error while waiting for cmdserver");
 	}
 	return NULL;
 }
 
 /* Connect to a cmdserver. Will start a new server on demand. */
 static hgclient_t *connectcmdserver(struct cmdserveropts *opts)
 {
 	const char *sockname = opts->redirectsockname[0] ?
 		opts->redirectsockname : opts->sockname;
 	debugmsg("try connect to %s", sockname);
 	hgclient_t *hgc = hgc_open(sockname);
 	if (hgc)
 		return hgc;
 
 	/* prevent us from being connected to an outdated server: we were
 	 * told by a server to redirect to opts->redirectsockname and that
 	 * address does not work. we do not want to connect to the server
 	 * again because it will probably tell us the same thing. */
 	if (sockname == opts->redirectsockname)
 		unlink(opts->sockname);
 
 	debugmsg("start cmdserver at %s", opts->initsockname);
 
 	pid_t pid = fork();
 	if (pid < 0)
 		abortmsg("failed to fork cmdserver process");
 	if (pid == 0) {
 		execcmdserver(opts);
 	} else {
 		hgc = retryconnectcmdserver(opts, pid);
 	}
 
 	return hgc;
 }
 
 static void killcmdserver(const struct cmdserveropts *opts)
 {
 	/* resolve config hash */
 	char *resolvedpath = realpath(opts->sockname, NULL);
 	if (resolvedpath) {
 		unlink(resolvedpath);
 		free(resolvedpath);
 	}
 }
 
 /* Run instructions sent from the server like unlink and set redirect path
  * Return 1 if reconnect is needed, otherwise 0 */
 static int runinstructions(struct cmdserveropts *opts, const char **insts)
 {
 	int needreconnect = 0;
 	if (!insts)
 		return needreconnect;
 
 	assert(insts);
 	opts->redirectsockname[0] = '\0';
 	const char **pinst;
 	for (pinst = insts; *pinst; pinst++) {
 		debugmsg("instruction: %s", *pinst);
 		if (strncmp(*pinst, "unlink ", 7) == 0) {
 			unlink(*pinst + 7);
 		} else if (strncmp(*pinst, "redirect ", 9) == 0) {
 			int r = snprintf(opts->redirectsockname,
 					 sizeof(opts->redirectsockname),
 					 "%s", *pinst + 9);
 			if (r < 0 || r >= (int)sizeof(opts->redirectsockname))
 				abortmsg("redirect path is too long (%d)", r);
 			needreconnect = 1;
 		} else if (strncmp(*pinst, "exit ", 5) == 0) {
 			int n = 0;
 			if (sscanf(*pinst + 5, "%d", &n) != 1)
 				abortmsg("cannot read the exit code");
 			exit(n);
 		} else if (strcmp(*pinst, "reconnect") == 0) {
 			needreconnect = 1;
 		} else {
 			abortmsg("unknown instruction: %s", *pinst);
 		}
 	}
 	return needreconnect;
 }
 
 /*
  * 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)
 		abortmsgerrno("failed to exec original hg");
 }
 
 int main(int argc, const char *argv[], const char *envp[])
 {
 	if (getenv("CHGDEBUG"))
 		enabledebugmsg();
 
 	if (!getenv("HGPLAIN") && isatty(fileno(stderr)))
 		enablecolor();
 
 	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) {
 		if (strcmp(argv[1], "--kill-chg-daemon") == 0) {
 			killcmdserver(&opts);
 			return 0;
 		}
 	}
 
 	hgclient_t *hgc;
 	size_t retry = 0;
 	while (1) {
 		hgc = connectcmdserver(&opts);
 		if (!hgc)
 			abortmsg("cannot open hg client");
 		hgc_setenv(hgc, envp);
 		const char **insts = hgc_validate(hgc, argv + 1, argc - 1);
 		int needreconnect = runinstructions(&opts, insts);
 		free(insts);
 		if (!needreconnect)
 			break;
 		hgc_close(hgc);
 		if (++retry > 10)
 			abortmsg("too many redirections.\n"
 				 "Please make sure %s is not a wrapper which "
 				 "changes sensitive environment variables "
 				 "before executing hg. If you have to use a "
 				 "wrapper, wrap chg instead of hg.",
 				 gethgcmd());
 	}
 
 	setupsignalhandler(hgc_peerpid(hgc), hgc_peerpgid(hgc));
 	int exitcode = hgc_runcommand(hgc, argv + 1, argc - 1);
 	restoresignalhandler();
 	hgc_close(hgc);
 	freecmdserveropts(&opts);
 	waitpager();
 
 	return exitcode;
 }