fs: Lock moved directories

When a directory is moved to a different directory, some filesystems
(udf, ext4, ocfs2, f2fs, and likely gfs2, reiserfs, and others) need to
update their pointer to the parent and this must not race with other
operations on the directory. Lock the directories when they are moved.
Although not all filesystems need this locking, we perform it in
vfs_rename() because getting the lock ordering right is really difficult
and we don't want to expose these locking details to filesystems.

CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20230601105830.13168-5-jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 14 insertions, 8 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 148570aabe74..6a5e26a529e1 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4731,7 +4731,7 @@ SYSCALL_DEFINE2(link, const char __user *, oldname, const char __user *, newname
  *	   sb->s_vfs_rename_mutex. We might be more accurate, but that's another
  *	   story.
  *	c) we have to lock _four_ objects - parents and victim (if it exists),
- *	   and source (if it is not a directory).
+ *	   and source.
  *	   And that - after we got ->i_mutex on parents (until then we don't know
  *	   whether the target exists).  Solution: try to be smart with locking
  *	   order for inodes.  We rely on the fact that tree topology may change
@@ -4815,10 +4815,16 @@ int vfs_rename(struct renamedata *rd)
 
 	take_dentry_name_snapshot(&old_name, old_dentry);
 	dget(new_dentry);
-	if (!is_dir || (flags & RENAME_EXCHANGE))
-		lock_two_nondirectories(source, target);
-	else if (target)
-		inode_lock(target);
+	/*
+	 * Lock all moved children. Moved directories may need to change parent
+	 * pointer so they need the lock to prevent against concurrent
+	 * directory changes moving parent pointer. For regular files we've
+	 * historically always done this. The lockdep locking subclasses are
+	 * somewhat arbitrary but RENAME_EXCHANGE in particular can swap
+	 * regular files and directories so it's difficult to tell which
+	 * subclasses to use.
+	 */
+	lock_two_inodes(source, target, I_MUTEX_NORMAL, I_MUTEX_NONDIR2);
 
 	error = -EPERM;
 	if (IS_SWAPFILE(source) || (target && IS_SWAPFILE(target)))
@@ -4866,9 +4872,9 @@ int vfs_rename(struct renamedata *rd)
 			d_exchange(old_dentry, new_dentry);
 	}
 out:
-	if (!is_dir || (flags & RENAME_EXCHANGE))
-		unlock_two_nondirectories(source, target);
-	else if (target)
+	if (source)
+		inode_unlock(source);
+	if (target)
 		inode_unlock(target);
 	dput(new_dentry);
 	if (!error) {