conf: switch mount_autodev() to new safe_mount_beneath() helper

src/lxc/conf.c

@@ -1051,50 +1051,55 @@ on_error:
 static int mount_autodev(const char *name, const struct lxc_rootfs *rootfs,
 			 int autodevtmpfssize, const char *lxcpath)
 {
-	__do_free char *path = NULL;
+	__do_close int root_mntpt_fd = -EBADF;
+	const char *path = rootfs->path ? rootfs->mount : NULL;
 	int ret;
-	size_t clen;
 	mode_t cur_mask;
         char mount_options[128];
 
 	INFO("Preparing \"/dev\"");
 
-	/* $(rootfs->mount) + "/dev/pts" + '\0' */
-	clen = (rootfs->path ? strlen(rootfs->mount) : 0) + 9;
-	path = must_realloc(NULL, clen);
 	sprintf(mount_options, "size=%d,mode=755", (autodevtmpfssize != 0) ? autodevtmpfssize : 500000);
 	DEBUG("Using mount options: %s", mount_options);
 
-	ret = snprintf(path, clen, "%s/dev", rootfs->path ? rootfs->mount : "");
-	if (ret < 0 || (size_t)ret >= clen)
-		return -1;
+	root_mntpt_fd = openat(-1, path, O_RDONLY | O_CLOEXEC | O_PATH | O_DIRECTORY);
+	if (root_mntpt_fd < 0)
+		return log_error_errno(-errno, errno, "Failed to open \"%s\"", path);
 
 	cur_mask = umask(S_IXUSR | S_IXGRP | S_IXOTH);
-	ret = mkdir(path, S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH);
+	ret = mkdirat(root_mntpt_fd, "dev" , S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH);
 	if (ret < 0 && errno != EEXIST) {
 		SYSERROR("Failed to create \"/dev\" directory");
 		ret = -errno;
 		goto reset_umask;
 	}
 
-	ret = safe_mount("none", "dev", "tmpfs", 0, mount_options,
-			 rootfs->path ? rootfs->mount : NULL );
+	ret = safe_mount_beneath(path, "none", "dev", "tmpfs", 0, mount_options);
 	if (ret < 0) {
-		SYSERROR("Failed to mount tmpfs on \"%s\"", path);
-		goto reset_umask;
-	}
-	TRACE("Mounted tmpfs on \"%s\"", path);
+		__do_free char *fallback_path = NULL;
 
-	ret = snprintf(path, clen, "%s/dev/pts", rootfs->path ? rootfs->mount : "");
-	if (ret < 0 || (size_t)ret >= clen) {
-		ret = -1;
-		goto reset_umask;
+		if (errno != ENOSYS) {
+			SYSERROR("Failed to mount tmpfs on \"%s\"", path);
+			goto reset_umask;
+		}
+
+		if (path) {
+			fallback_path = must_make_path(path, "/dev", NULL);
+			ret = safe_mount("none", fallback_path, "tmpfs", 0, mount_options, path);
+		} else {
+			ret = safe_mount("none", "dev", "tmpfs", 0, mount_options, NULL);
+		}
+		if (ret < 0) {
+			SYSERROR("Failed to mount tmpfs on \"%s\"", path);
+			goto reset_umask;
+		}
 	}
+	TRACE("Mounted tmpfs on \"%s\"", path);
 
 	/* If we are running on a devtmpfs mapping, dev/pts may already exist.
 	 * If not, then create it and exit if that fails...
 	 */
-	ret = mkdir(path, S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH);
+	ret = mkdirat(root_mntpt_fd, "dev/pts", S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH);
 	if (ret < 0 && errno != EEXIST) {
 		SYSERROR("Failed to create directory \"%s\"", path);
 		ret = -errno;