Hi Amir,
On Sun, Jan 5, 2025 at 4:24 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote:
>
> Dmitry Safonov reported that a WARN_ON() assertion can be trigered by
> userspace when calling inotify_show_fdinfo() for an overlayfs watched
> inode, whose dentry aliases were discarded with drop_caches.
>
> The WARN_ON() assertion in inotify_show_fdinfo() was removed, because
> it is possible for encoding file handle to fail for other reason, but
> the impact of failing to encode an overlayfs file handle goes beyond
> this assertion.
>
> As shown in the LTP test case mentioned in the link below, failure to
> encode an overlayfs file handle from a non-aliased inode also leads to
> failure to report an fid with FAN_DELETE_SELF fanotify events.
>
> As Dmitry notes in his analyzis of the problem, ovl_encode_fh() fails
> if it cannot find an alias for the inode, but this failure can be fixed.
> ovl_encode_fh() seldom uses the alias and in the case of non-decodable
> file handles, as is often the case with fanotify fid info,
> ovl_encode_fh() never needs to use the alias to encode a file handle.
>
> Defer finding an alias until it is actually needed so ovl_encode_fh()
> will not fail in the common case of FAN_DELETE_SELF fanotify events.
>
> Fixes: 16aac5ad1fa9 ("ovl: support encoding non-decodable file handles")
> Reported-by: Dmitry Safonov <dima@xxxxxxxxxx>
> Closes: https://lore.kernel.org/linux-fsdevel/CAOQ4uxiie81voLZZi2zXS1BziXZCM24nXqPAxbu8kxXCUWdwOg@xxxxxxxxxxxxxx/
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
Thank you for such a quick and proper fix, even though it was the
holiday season :-)
FWIW, I've pushed the patches locally. In two or three days I should
have some hundreds of test results from the duts where the issue was
hitting originally. Judging by code changes, I hardly doubt the
original issue would reproduce, but might be worth getting more
coverage of this code.
Thanks,
Dmitry
