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;
 
@@ -464,12 +467,45 @@ 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;
+	if (!pid) {
+		char uid_buf[32];
+		char *arguments[] = {
+			"getent",
+			"passwd",
+			uid_buf,
+			NULL
+		};
+
+		close(pipes[0]);
+
+		/* We want to capture stdout. */
+		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_devnull();
+		if (fd < 0) {
+			close(STDIN_FILENO);
+			close(STDERR_FILENO);
+		} else {
+			(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 || ret >= sizeof(uid_buf))
+			exit(EXIT_FAILURE);
+
+		/* Try to run getent program. */
+		(void)execvp("getent", arguments);
+		exit(EXIT_FAILURE);
+	}
 
 	close(pipes[1]);
 
@@ -495,23 +531,28 @@ static char *lxc_attach_getpwshell(uid_t uid)
 		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)
+		if (!token || !endptr || *endptr || value == LONG_MIN ||
+				value == LONG_MAX)
 			continue;
+
 		/* dummy sanity check: user id matches */
-			if ((uid_t) value != uid)
+		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;
+				continue;
 		}
 		if (!token)
 			continue;
@@ -523,30 +564,13 @@ static char *lxc_attach_getpwshell(uid_t uid)
 		if (token)
 			continue;
 
-			found = 1;
+		found = true;
 	}
-
 	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) {
+	ret = wait_for_pid(pid);
+	if (ret < 0) {
 		free(result);
 		return NULL;
 	}
@@ -557,43 +581,6 @@ static char *lxc_attach_getpwshell(uid_t uid)
 	}
 
 	return result;
-	} else {
-		char uid_buf[32];
-		char *arguments[] = {
-			"getent",
-			"passwd",
-			uid_buf,
-			NULL
-		};
-
-		close(pipes[0]);
-
-		/* We want to capture stdout. */
-		dup2(pipes[1], 1);
-		close(pipes[1]);
-
-		/* Get rid of stdin/stderr, so we try to associate it with
-		 * /dev/null.
-		 */
-		fd = open("/dev/null", O_RDWR);
-		if (fd < 0) {
-			close(0);
-			close(2);
-		} else {
-			dup2(fd, 0);
-			dup2(fd, 2);
-			close(fd);
-		}
-
-		/* Finish argument list. */
-		ret = snprintf(uid_buf, sizeof(uid_buf), "%ld", (long) uid);
-		if (ret <= 0)
-			exit(-1);
-
-		/* Try to run getent program. */
-		(void) execvp("getent", arguments);
-		exit(-1);
-	}
 }
 
 static void lxc_attach_get_init_uidgid(uid_t *init_uid, gid_t *init_gid)