auth.c

@@ -720,158 +720,6 @@ auth_get_canonical_hostname(struct ssh *ssh, int use_dns)
 	}
 }
 
-/*
- * Runs command in a subprocess with a minimal environment.
- * Returns pid on success, 0 on failure.
- * The child stdout and stderr maybe captured, left attached or sent to
- * /dev/null depending on the contents of flags.
- * "tag" is prepended to log messages.
- * NB. "command" is only used for logging; the actual command executed is
- * av[0].
- */
-pid_t
-subprocess(const char *tag, struct passwd *pw, const char *command,
-    int ac, char **av, FILE **child, u_int flags)
-{
-	FILE *f = NULL;
-	struct stat st;
-	int fd, devnull, p[2], i;
-	pid_t pid;
-	char *cp, errmsg[512];
-	u_int envsize;
-	char **child_env;
-
-	if (child != NULL)
-		*child = NULL;
-
-	debug3_f("%s command \"%s\" running as %s (flags 0x%x)",
-	    tag, command, pw->pw_name, flags);
-
-	/* Check consistency */
-	if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0 &&
-	    (flags & SSH_SUBPROCESS_STDOUT_CAPTURE) != 0) {
-		error_f("inconsistent flags");
-		return 0;
-	}
-	if (((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) == 0) != (child == NULL)) {
-		error_f("inconsistent flags/output");
-		return 0;
-	}
-
-	/*
-	 * If executing an explicit binary, then verify the it exists
-	 * and appears safe-ish to execute
-	 */
-	if (!path_absolute(av[0])) {
-		error("%s path is not absolute", tag);
-		return 0;
-	}
-	temporarily_use_uid(pw);
-	if (stat(av[0], &st) == -1) {
-		error("Could not stat %s \"%s\": %s", tag,
-		    av[0], strerror(errno));
-		restore_uid();
-		return 0;
-	}
-	if (safe_path(av[0], &st, NULL, 0, errmsg, sizeof(errmsg)) != 0) {
-		error("Unsafe %s \"%s\": %s", tag, av[0], errmsg);
-		restore_uid();
-		return 0;
-	}
-	/* Prepare to keep the child's stdout if requested */
-	if (pipe(p) == -1) {
-		error("%s: pipe: %s", tag, strerror(errno));
-		restore_uid();
-		return 0;
-	}
-	restore_uid();
-
-	switch ((pid = fork())) {
-	case -1: /* error */
-		error("%s: fork: %s", tag, strerror(errno));
-		close(p[0]);
-		close(p[1]);
-		return 0;
-	case 0: /* child */
-		/* Prepare a minimal environment for the child. */
-		envsize = 5;
-		child_env = xcalloc(sizeof(*child_env), envsize);
-		child_set_env(&child_env, &envsize, "PATH", _PATH_STDPATH);
-		child_set_env(&child_env, &envsize, "USER", pw->pw_name);
-		child_set_env(&child_env, &envsize, "LOGNAME", pw->pw_name);
-		child_set_env(&child_env, &envsize, "HOME", pw->pw_dir);
-		if ((cp = getenv("LANG")) != NULL)
-			child_set_env(&child_env, &envsize, "LANG", cp);
-
-		for (i = 0; i < NSIG; i++)
-			ssh_signal(i, SIG_DFL);
-
-		if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
-			error("%s: open %s: %s", tag, _PATH_DEVNULL,
-			    strerror(errno));
-			_exit(1);
-		}
-		if (dup2(devnull, STDIN_FILENO) == -1) {
-			error("%s: dup2: %s", tag, strerror(errno));
-			_exit(1);
-		}
-
-		/* Set up stdout as requested; leave stderr in place for now. */
-		fd = -1;
-		if ((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) != 0)
-			fd = p[1];
-		else if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0)
-			fd = devnull;
-		if (fd != -1 && dup2(fd, STDOUT_FILENO) == -1) {
-			error("%s: dup2: %s", tag, strerror(errno));
-			_exit(1);
-		}
-		closefrom(STDERR_FILENO + 1);
-
-		/* Don't use permanently_set_uid() here to avoid fatal() */
-		if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) == -1) {
-			error("%s: setresgid %u: %s", tag, (u_int)pw->pw_gid,
-			    strerror(errno));
-			_exit(1);
-		}
-		if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) == -1) {
-			error("%s: setresuid %u: %s", tag, (u_int)pw->pw_uid,
-			    strerror(errno));
-			_exit(1);
-		}
-		/* stdin is pointed to /dev/null at this point */
-		if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0 &&
-		    dup2(STDIN_FILENO, STDERR_FILENO) == -1) {
-			error("%s: dup2: %s", tag, strerror(errno));
-			_exit(1);
-		}
-
-		execve(av[0], av, child_env);
-		error("%s exec \"%s\": %s", tag, command, strerror(errno));
-		_exit(127);
-	default: /* parent */
-		break;
-	}
-
-	close(p[1]);
-	if ((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) == 0)
-		close(p[0]);
-	else if ((f = fdopen(p[0], "r")) == NULL) {
-		error("%s: fdopen: %s", tag, strerror(errno));
-		close(p[0]);
-		/* Don't leave zombie child */
-		kill(pid, SIGTERM);
-		while (waitpid(pid, NULL, 0) == -1 && errno == EINTR)
-			;
-		return 0;
-	}
-	/* Success */
-	debug3_f("%s pid %ld", tag, (long)pid);
-	if (child != NULL)
-		*child = f;
-	return pid;
-}
-
 /* These functions link key/cert options to the auth framework */
 
 /* Log sshauthopt options locally and (optionally) for remote transmission */

auth.h

@@ -206,10 +206,4 @@ void	 auth_debug_reset(void);
 
 struct passwd *fakepw(void);
 
-#define	SSH_SUBPROCESS_STDOUT_DISCARD  (1)     /* Discard stdout */
-#define	SSH_SUBPROCESS_STDOUT_CAPTURE  (1<<1)  /* Redirect stdout */
-#define	SSH_SUBPROCESS_STDERR_DISCARD  (1<<2)  /* Discard stderr */
-pid_t	subprocess(const char *, struct passwd *,
-    const char *, int, char **, FILE **, u_int flags);
-
 #endif

auth2-pubkey.c

@@ -527,9 +527,10 @@ match_principals_command(struct ssh *ssh, struct passwd *user_pw,
 	/* Prepare a printable command for logs, etc. */
 	command = argv_assemble(ac, av);
 
-	if ((pid = subprocess("AuthorizedPrincipalsCommand", runas_pw, command,
+	if ((pid = subprocess("AuthorizedPrincipalsCommand", command,
 	    ac, av, &f,
-	    SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD)) == 0)
+	    SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD,
+	    runas_pw, temporarily_use_uid, restore_uid)) == 0)
 		goto out;
 
 	uid_swapped = 1;
@@ -965,9 +966,10 @@ user_key_command_allowed2(struct ssh *ssh, struct passwd *user_pw,
 		xasprintf(&command, "%s %s", av[0], av[1]);
 	}
 
-	if ((pid = subprocess("AuthorizedKeysCommand", runas_pw, command,
+	if ((pid = subprocess("AuthorizedKeysCommand", command,
 	    ac, av, &f,
-	    SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD)) == 0)
+	    SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD,
+	    runas_pw, temporarily_use_uid, restore_uid)) == 0)
 		goto out;
 
 	uid_swapped = 1;

misc.c

@@ -2378,3 +2378,172 @@ stdfd_devnull(int do_stdin, int do_stdout, int do_stderr)
 		close(devnull);
 	return ret;
 }
+
+/*
+ * Runs command in a subprocess with a minimal environment.
+ * Returns pid on success, 0 on failure.
+ * The child stdout and stderr maybe captured, left attached or sent to
+ * /dev/null depending on the contents of flags.
+ * "tag" is prepended to log messages.
+ * NB. "command" is only used for logging; the actual command executed is
+ * av[0].
+ */
+pid_t
+subprocess(const char *tag, const char *command,
+    int ac, char **av, FILE **child, u_int flags,
+    struct passwd *pw, privdrop_fn *drop_privs, privrestore_fn *restore_privs)
+{
+	FILE *f = NULL;
+	struct stat st;
+	int fd, devnull, p[2], i;
+	pid_t pid;
+	char *cp, errmsg[512];
+	u_int nenv = 0;
+	char **env = NULL;
+
+	/* If dropping privs, then must specify user and restore function */
+	if (drop_privs != NULL && (pw == NULL || restore_privs == NULL)) {
+		error("%s: inconsistent arguments", tag); /* XXX fatal? */
+		return SSH_ERR_INVALID_ARGUMENT;
+	}
+	if (pw == NULL && (pw = getpwuid(getuid())) == NULL) {
+		error("%s: no user for current uid", tag);
+		return SSH_ERR_INVALID_ARGUMENT;
+	}
+	if (child != NULL)
+		*child = NULL;
+
+	debug3_f("%s command \"%s\" running as %s (flags 0x%x)",
+	    tag, command, pw->pw_name, flags);
+
+	/* Check consistency */
+	if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0 &&
+	    (flags & SSH_SUBPROCESS_STDOUT_CAPTURE) != 0) {
+		error_f("inconsistent flags");
+		return 0;
+	}
+	if (((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) == 0) != (child == NULL)) {
+		error_f("inconsistent flags/output");
+		return 0;
+	}
+
+	/*
+	 * If executing an explicit binary, then verify the it exists
+	 * and appears safe-ish to execute
+	 */
+	if (!path_absolute(av[0])) {
+		error("%s path is not absolute", tag);
+		return 0;
+	}
+	if (drop_privs != NULL)
+		drop_privs(pw);
+	if (stat(av[0], &st) == -1) {
+		error("Could not stat %s \"%s\": %s", tag,
+		    av[0], strerror(errno));
+		goto restore_return;
+	}
+	if ((flags & SSH_SUBPROCESS_UNSAFE_PATH) == 0 &&
+	    safe_path(av[0], &st, NULL, 0, errmsg, sizeof(errmsg)) != 0) {
+		error("Unsafe %s \"%s\": %s", tag, av[0], errmsg);
+		goto restore_return;
+	}
+	/* Prepare to keep the child's stdout if requested */
+	if (pipe(p) == -1) {
+		error("%s: pipe: %s", tag, strerror(errno));
+ restore_return:
+		if (restore_privs != NULL)
+			restore_privs();
+		return 0;
+	}
+	if (restore_privs != NULL)
+		restore_privs();
+
+	switch ((pid = fork())) {
+	case -1: /* error */
+		error("%s: fork: %s", tag, strerror(errno));
+		close(p[0]);
+		close(p[1]);
+		return 0;
+	case 0: /* child */
+		/* Prepare a minimal environment for the child. */
+		if ((flags & SSH_SUBPROCESS_PRESERVE_ENV) == 0) {
+			nenv = 5;
+			env = xcalloc(sizeof(*env), nenv);
+			child_set_env(&env, &nenv, "PATH", _PATH_STDPATH);
+			child_set_env(&env, &nenv, "USER", pw->pw_name);
+			child_set_env(&env, &nenv, "LOGNAME", pw->pw_name);
+			child_set_env(&env, &nenv, "HOME", pw->pw_dir);
+			if ((cp = getenv("LANG")) != NULL)
+				child_set_env(&env, &nenv, "LANG", cp);
+		}
+
+		for (i = 0; i < NSIG; i++)
+			ssh_signal(i, SIG_DFL);
+
+		if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
+			error("%s: open %s: %s", tag, _PATH_DEVNULL,
+			    strerror(errno));
+			_exit(1);
+		}
+		if (dup2(devnull, STDIN_FILENO) == -1) {
+			error("%s: dup2: %s", tag, strerror(errno));
+			_exit(1);
+		}
+
+		/* Set up stdout as requested; leave stderr in place for now. */
+		fd = -1;
+		if ((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) != 0)
+			fd = p[1];
+		else if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0)
+			fd = devnull;
+		if (fd != -1 && dup2(fd, STDOUT_FILENO) == -1) {
+			error("%s: dup2: %s", tag, strerror(errno));
+			_exit(1);
+		}
+		closefrom(STDERR_FILENO + 1);
+
+		if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) == -1) {
+			error("%s: setresgid %u: %s", tag, (u_int)pw->pw_gid,
+			    strerror(errno));
+			_exit(1);
+		}
+		if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) == -1) {
+			error("%s: setresuid %u: %s", tag, (u_int)pw->pw_uid,
+			    strerror(errno));
+			_exit(1);
+		}
+		/* stdin is pointed to /dev/null at this point */
+		if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0 &&
+		    dup2(STDIN_FILENO, STDERR_FILENO) == -1) {
+			error("%s: dup2: %s", tag, strerror(errno));
+			_exit(1);
+		}
+		if (env != NULL)
+			execve(av[0], av, env);
+		else
+			execv(av[0], av);
+		error("%s %s \"%s\": %s", tag, env == NULL ? "execv" : "execve",
+		    command, strerror(errno));
+		_exit(127);
+	default: /* parent */
+		break;
+	}
+
+	close(p[1]);
+	if ((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) == 0)
+		close(p[0]);
+	else if ((f = fdopen(p[0], "r")) == NULL) {
+		error("%s: fdopen: %s", tag, strerror(errno));
+		close(p[0]);
+		/* Don't leave zombie child */
+		kill(pid, SIGTERM);
+		while (waitpid(pid, NULL, 0) == -1 && errno == EINTR)
+			;
+		return 0;
+	}
+	/* Success */
+	debug3_f("%s pid %ld", tag, (long)pid);
+	if (child != NULL)
+		*child = f;
+	return pid;
+}

misc.h

@@ -97,6 +97,16 @@ int	 stdfd_devnull(int, int, int);
 struct passwd *pwcopy(struct passwd *);
 const char *ssh_gai_strerror(int);
 
+typedef void privdrop_fn(struct passwd *);
+typedef void privrestore_fn(void);
+#define	SSH_SUBPROCESS_STDOUT_DISCARD	(1)     /* Discard stdout */
+#define	SSH_SUBPROCESS_STDOUT_CAPTURE	(1<<1)  /* Redirect stdout */
+#define	SSH_SUBPROCESS_STDERR_DISCARD	(1<<2)  /* Discard stderr */
+#define	SSH_SUBPROCESS_UNSAFE_PATH	(1<<3)	/* Don't check for safe cmd */
+#define	SSH_SUBPROCESS_PRESERVE_ENV	(1<<4)	/* Keep parent environment */
+pid_t subprocess(const char *, const char *, int, char **, FILE **, u_int,
+    struct passwd *, privdrop_fn *, privrestore_fn *);
+
 typedef struct arglist arglist;
 struct arglist {
 	char    **list;