linux-cve-announce - CVE-2024-57924: fs: relax assertions on failure to encode file handles

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Message-ID: <2025011943-CVE-2024-57924-954a@gregkh>
Date: Sun, 19 Jan 2025 12:52:55 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-57924: fs: relax assertions on failure to encode file handles

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

fs: relax assertions on failure to encode file handles

Encoding file handles is usually performed by a filesystem >encode_fh()
method that may fail for various reasons.

The legacy users of exportfs_encode_fh(), namely, nfsd and
name_to_handle_at(2) syscall are ready to cope with the possibility
of failure to encode a file handle.

There are a few other users of exportfs_encode_{fh,fid}() that
currently have a WARN_ON() assertion when ->encode_fh() fails.
Relax those assertions because they are wrong.

The second linked bug report states commit 16aac5ad1fa9 ("ovl: support
encoding non-decodable file handles") in v6.6 as the regressing commit,
but this is not accurate.

The aforementioned commit only increases the chances of the assertion
and allows triggering the assertion with the reproducer using overlayfs,
inotify and drop_caches.

Triggering this assertion was always possible with other filesystems and
other reasons of ->encode_fh() failures and more particularly, it was
also possible with the exact same reproducer using overlayfs that is
mounted with options index=on,nfs_export=on also on kernels < v6.6.
Therefore, I am not listing the aforementioned commit as a Fixes commit.

Backport hint: this patch will have a trivial conflict applying to
v6.6.y, and other trivial conflicts applying to stable kernels < v6.6.

The Linux kernel CVE team has assigned CVE-2024-57924 to this issue.

Affected and fixed versions
===========================

	Fixed in 6.12.10 with commit adcde2872f8fc399b249758ae1990dcd53b694ea
	Fixed in 6.13-rc7 with commit 974e3fe0ac61de85015bbe5a4990cf4127b304b2

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-57924
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	fs/notify/fdinfo.c
	fs/overlayfs/copy_up.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/adcde2872f8fc399b249758ae1990dcd53b694ea
	https://git.kernel.org/stable/c/974e3fe0ac61de85015bbe5a4990cf4127b304b2