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kernfs: annotate different lockdep class for of->mutex of writable files 

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: 0fedefd4c4 ("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>
This commit is contained in:
Amir Goldstein 2024-04-05 17:56:35 +03:00 committed by Al Viro
parent fec50db703
commit 16b52bbee4
1 changed files with 8 additions and 1 deletions
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9
fs/kernfs/file.c
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@ -636,11 +636,18 @@ static int kernfs_fop_open(struct inode *inode, struct file *file)
* 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);