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commit c45beebfde34aa71afbc48b2c54cdda623515037 upstream.
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: 16aac5ad1f ("ovl: support encoding non-decodable file handles")
Reported-by: Dmitry Safonov <dima@arista.com>
Closes: https://lore.kernel.org/linux-fsdevel/CAOQ4uxiie81voLZZi2zXS1BziXZCM24nXqPAxbu8kxXCUWdwOg@mail.gmail.com/
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/r/20250105162404.357058-3-amir73il@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.