[PATCH 6.8 150/172] kernfs: annotate different lockdep class for of->mutex of writable files

Greg Kroah-Hartman
2024-04-15T14:30:59Z

From: Amir Goldstein <amir73il@gmail.com>

commit 16b52bbee4823b01ab7fe3919373c981a38f3797 upstream.

The writable file /sys/power/resume may call vfs lookup helpers for
arbitrary paths and readonly files can be read by overlayfs from vfs
helpers when sysfs is a lower layer of overalyfs.

To avoid a lockdep warning of circular dependency between overlayfs
inode lock and kernfs of->mutex, use a different lockdep class for
writable and readonly kernfs files.

Reported-by: syzbot+9a5b0ced8b1bfb238b56@syzkaller.appspotmail.com
Fixes: 0fedefd4c4e3 ("kernfs: sysfs: support custom llseek method for sysfs entries")
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/kernfs/file.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -634,11 +634,18 @@ static int kernfs_fop_open(struct inode
* each file a separate locking class. Let's differentiate on
* whether the file has mmap or not for now.
*
- * Both paths of the branch look the same. They're supposed to
+ * For similar reasons, writable and readonly files are given different
+ * lockdep key, because the writable file /sys/power/resume may call vfs
+ * lookup helpers for arbitrary paths and readonly files can be read by
+ * overlayfs from vfs helpers when sysfs is a lower layer of overalyfs.
+ *
+ * All three cases look the same. They're supposed to
* look that way and give @of->mutex different static lockdep keys.
*/
if (has_mmap)
mutex_init(&of->mutex);
+ else if (file->f_mode & FMODE_WRITE)
+ mutex_init(&of->mutex);
else
mutex_init(&of->mutex);