[PATCH 1/6] btrfs-progs: enhance btrfs_mkdir() function

[Qu Wenruo <wqu@suse.com>]

The function btrfs_mkdir() is currently only utilized by btrfs check, to
create the lost+found directory.

However we're going to add extra callers for this function, to create
directories (and subvolumes) for the incoming "mkfs.btrfs --subvolume"
option.

Thus here we want extra checks for the @parent_ino:

- Make sure the parent inode exists
- Make sure the parent inode is indeed a directory

And since we're here, also convert the @path to a on-stack one to
prevent memory leakage.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 kernel-shared/inode.c | 53 +++++++++++++++++++++++++++++--------------
 1 file changed, 36 insertions(+), 17 deletions(-)

diff --git a/kernel-shared/inode.c b/kernel-shared/inode.c
index 3d420787c8f9..50bb460acc79 100644
--- a/kernel-shared/inode.c
+++ b/kernel-shared/inode.c
@@ -526,18 +526,41 @@ int btrfs_mkdir(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 		char *name, int namelen, u64 parent_ino, u64 *ino, int mode)
 {
 	struct btrfs_dir_item *dir_item;
-	struct btrfs_path *path;
+	struct btrfs_path path = { 0 };
+	struct btrfs_key key;
+	struct btrfs_inode_item *iitem;
 	u64 ret_ino = 0;
 	int ret = 0;
 
-	path = btrfs_alloc_path();
-	if (!path)
-		return -ENOMEM;
-
 	if (ino && *ino)
 		ret_ino = *ino;
 
-	dir_item = btrfs_lookup_dir_item(NULL, root, path, parent_ino,
+	/* Make sure the parent inode exists and is a directory. */
+	key.objectid = parent_ino;
+	key.type = BTRFS_INODE_ITEM_KEY;
+	key.offset = 0;
+	ret = btrfs_lookup_inode(NULL, root, &path, &key, 0);
+	if (ret > 0) {
+		ret = -ENOENT;
+		/* Fallthrough */
+	}
+	if (ret < 0) {
+		errno = -ret;
+		error("failed to lookup inode %llu in root %lld: %m",
+		      parent_ino, root->root_key.objectid);
+		goto out;
+	}
+	iitem = btrfs_item_ptr(path.nodes[0], path.slots[0], struct btrfs_inode_item);
+	if (!S_ISDIR(btrfs_inode_mode(path.nodes[0], iitem))) {
+		ret = -EUCLEAN;
+		errno = -ret;
+		error("inode %llu in root %lld is not a directory", parent_ino,
+		      root->root_key.objectid);
+		goto out;
+	}
+	btrfs_release_path(&path);
+
+	dir_item = btrfs_lookup_dir_item(NULL, root, &path, parent_ino,
 					 name, namelen, 0);
 	if (IS_ERR(dir_item)) {
 		ret = PTR_ERR(dir_item);
@@ -551,23 +574,19 @@ int btrfs_mkdir(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 		 * Already have conflicting name, check if it is a dir.
 		 * Either way, no need to continue.
 		 */
-		btrfs_dir_item_key_to_cpu(path->nodes[0], dir_item, &found_key);
+		btrfs_dir_item_key_to_cpu(path.nodes[0], dir_item, &found_key);
 		ret_ino = found_key.objectid;
-		if (btrfs_dir_ftype(path->nodes[0], dir_item) != BTRFS_FT_DIR)
+		if (btrfs_dir_ftype(path.nodes[0], dir_item) != BTRFS_FT_DIR)
 			ret = -EEXIST;
 		goto out;
 	}
 
-	if (!ret_ino)
-		/*
-		 * This is *UNSAFE* if some leaf is corrupted,
-		 * only used as a fallback method. Caller should either
-		 * ensure the fs is OK or pass ino with unused inode number.
-		 */
+	if (!ret_ino) {
 		ret = btrfs_find_free_objectid(NULL, root, parent_ino,
 					       &ret_ino);
-	if (ret)
-		goto out;
+		if (ret)
+			goto out;
+	}
 	ret = btrfs_new_inode(trans, root, ret_ino, mode | S_IFDIR);
 	if (ret)
 		goto out;
@@ -576,7 +595,7 @@ int btrfs_mkdir(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 	if (ret)
 		goto out;
 out:
-	btrfs_free_path(path);
+	btrfs_release_path(&path);
 	if (ret == 0 && ino)
 		*ino = ret_ino;
 	return ret;
-- 
2.42.0