attach: simplify lxc_attach_getpwshell()

src/lxc/attach.c

@@ -448,12 +448,15 @@ static char *lxc_attach_getpwshell(uid_t uid)
 	int fd, ret;
 	pid_t pid;
 	int pipes[2];
-	char *result = NULL;
+	FILE *pipe_f;
+	bool found = false;
+	size_t line_bufsz = 0;
+	char *line = NULL, *result = NULL;
 
 	/* We need to fork off a process that runs the getent program, and we
 	 * need to capture its output, so we use a pipe for that purpose.
 	 */
-	ret = pipe(pipes);
+	ret = pipe2(pipes, O_CLOEXEC);
 	if (ret < 0)
 		return NULL;
 
@@ -464,100 +467,7 @@ static char *lxc_attach_getpwshell(uid_t uid)
 		return NULL;
 	}
 
-	if (pid) {
-		int status;
-		FILE *pipe_f;
-		int found = 0;
-		size_t line_bufsz = 0;
-		char *line = NULL;
-
-		close(pipes[1]);
-
-		pipe_f = fdopen(pipes[0], "r");
-		while (getline(&line, &line_bufsz, pipe_f) != -1) {
-			int i;
-			long value;
-			char *token;
-			char *endptr = NULL, *saveptr = NULL;
-
-			/* If we already found something, just continue to read
-			 * until the pipe doesn't deliver any more data, but
-			 * don't modify the existing data structure.
-			 */
-			if (found)
-				continue;
-
-			/* Trim line on the right hand side. */
-			for (i = strlen(line); i > 0 && (line[i - 1] == '\n' || line[i - 1] == '\r'); --i)
-				line[i - 1] = '\0';
-
-			/* Split into tokens: first: user name. */
-			token = strtok_r(line, ":", &saveptr);
-			if (!token)
-				continue;
-			/* next: dummy password field */
-			token = strtok_r(NULL, ":", &saveptr);
-			if (!token)
-				continue;
-			/* next: user id */
-			token = strtok_r(NULL, ":", &saveptr);
-			value = token ? strtol(token, &endptr, 10) : 0;
-			if (!token || !endptr || *endptr || value == LONG_MIN || value == LONG_MAX)
-				continue;
-			/* dummy sanity check: user id matches */
-			if ((uid_t) value != uid)
-				continue;
-			/* skip fields: gid, gecos, dir, go to next field 'shell' */
-			for (i = 0; i < 4; i++) {
-				token = strtok_r(NULL, ":", &saveptr);
-				if (!token)
-					break;
-			}
-			if (!token)
-				continue;
-			free(result);
-			result = strdup(token);
-
-			/* Sanity check that there are no fields after that. */
-			token = strtok_r(NULL, ":", &saveptr);
-			if (token)
-				continue;
-
-			found = 1;
-		}
-
-		free(line);
-		fclose(pipe_f);
-	again:
-		if (waitpid(pid, &status, 0) < 0) {
-			if (errno == EINTR)
-				goto again;
-			free(result);
-			return NULL;
-		}
-
-		/* Some sanity checks. If anything even hinted at going wrong,
-		 * we can't be sure we have a valid result, so we assume we
-		 * don't.
-		 */
-
-		if (!WIFEXITED(status)) {
-			free(result);
-			return NULL;
-		}
-
-		if (WEXITSTATUS(status) != 0) {
-			free(result);
-			return NULL;
-		}
-
-		if (!found) {
-			free(result);
-			return NULL;
-		}
-
-		return result;
-	} else {
+	if (!pid) {
 		char uid_buf[32];
 		char *arguments[] = {
 			"getent",
@@ -569,31 +479,108 @@ static char *lxc_attach_getpwshell(uid_t uid)
 		close(pipes[0]);
 
 		/* We want to capture stdout. */
-		dup2(pipes[1], 1);
+		ret = dup2(pipes[1], STDOUT_FILENO);
 		close(pipes[1]);
+		if (ret < 0)
+			exit(EXIT_FAILURE);
 
 		/* Get rid of stdin/stderr, so we try to associate it with
 		 * /dev/null.
 		 */
-		fd = open("/dev/null", O_RDWR);
+		fd = open_devnull();
 		if (fd < 0) {
-			close(0);
-			close(2);
+			close(STDIN_FILENO);
+			close(STDERR_FILENO);
 		} else {
-			dup2(fd, 0);
-			dup2(fd, 2);
+			(void)dup3(fd, STDIN_FILENO, O_CLOEXEC);
+			(void)dup3(fd, STDOUT_FILENO, O_CLOEXEC);
 			close(fd);
 		}
 
 		/* Finish argument list. */
-		ret = snprintf(uid_buf, sizeof(uid_buf), "%ld", (long) uid);
-		if (ret <= 0)
-			exit(-1);
+		ret = snprintf(uid_buf, sizeof(uid_buf), "%ld", (long)uid);
+		if (ret <= 0 || ret >= sizeof(uid_buf))
+			exit(EXIT_FAILURE);
 
 		/* Try to run getent program. */
-		(void) execvp("getent", arguments);
-		exit(-1);
+		(void)execvp("getent", arguments);
+		exit(EXIT_FAILURE);
 	}
+
+	close(pipes[1]);
+
+	pipe_f = fdopen(pipes[0], "r");
+	while (getline(&line, &line_bufsz, pipe_f) != -1) {
+		int i;
+		long value;
+		char *token;
+		char *endptr = NULL, *saveptr = NULL;
+
+		/* If we already found something, just continue to read
+		* until the pipe doesn't deliver any more data, but
+		* don't modify the existing data structure.
+		 */
+		if (found)
+			continue;
+
+		/* Trim line on the right hand side. */
+		for (i = strlen(line); i > 0 && (line[i - 1] == '\n' || line[i - 1] == '\r'); --i)
+			line[i - 1] = '\0';
+
+		/* Split into tokens: first: user name. */
+		token = strtok_r(line, ":", &saveptr);
+		if (!token)
+			continue;
+
+		/* next: dummy password field */
+		token = strtok_r(NULL, ":", &saveptr);
+		if (!token)
+			continue;
+
+		/* next: user id */
+		token = strtok_r(NULL, ":", &saveptr);
+		value = token ? strtol(token, &endptr, 10) : 0;
+		if (!token || !endptr || *endptr || value == LONG_MIN ||
+				value == LONG_MAX)
+			continue;
+
+		/* dummy sanity check: user id matches */
+		if ((uid_t)value != uid)
+			continue;
+
+		/* skip fields: gid, gecos, dir, go to next field 'shell' */
+		for (i = 0; i < 4; i++) {
+			token = strtok_r(NULL, ":", &saveptr);
+			if (!token)
+				continue;
+		}
+		if (!token)
+			continue;
+		free(result);
+		result = strdup(token);
+
+		/* Sanity check that there are no fields after that. */
+		token = strtok_r(NULL, ":", &saveptr);
+		if (token)
+			continue;
+
+		found = true;
+	}
+	free(line);
+	fclose(pipe_f);
+
+	ret = wait_for_pid(pid);
+	if (ret < 0) {
+		free(result);
+		return NULL;
+	}
+
+	if (!found) {
+		free(result);
+		return NULL;
+	}
+
+	return result;
 }
 
 static void lxc_attach_get_init_uidgid(uid_t *init_uid, gid_t *init_gid)