cve/published/2024/CVE-2024-57952.mbox

From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: <linux-cve-announce@vger.kernel.org>
Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org>
Subject: CVE-2024-57952: Revert "libfs: fix infinite directory reads for offset dir"

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

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

Revert "libfs: fix infinite directory reads for offset dir"

The current directory offset allocator (based on mtree_alloc_cyclic)
stores the next offset value to return in octx->next_offset. This
mechanism typically returns values that increase monotonically over
time. Eventually, though, the newly allocated offset value wraps
back to a low number (say, 2) which is smaller than other already-
allocated offset values.

Yu Kuai <yukuai3@huawei.com> reports that, after commit 64a7ce76fb90
("libfs: fix infinite directory reads for offset dir"), if a
directory's offset allocator wraps, existing entries are no longer
visible via readdir/getdents because offset_readdir() stops listing
entries once an entry's offset is larger than octx->next_offset.
These entries vanish persistently -- they can be looked up, but will
never again appear in readdir(3) output.

The reason for this is that the commit treats directory offsets as
monotonically increasing integer values rather than opaque cookies,
and introduces this comparison:

	if (dentry2offset(dentry) >= last_index) {

On 64-bit platforms, the directory offset value upper bound is
2^63 - 1. Directory offsets will monotonically increase for millions
of years without wrapping.

On 32-bit platforms, however, LONG_MAX is 2^31 - 1. The allocator
can wrap after only a few weeks (at worst).

Revert commit 64a7ce76fb90 ("libfs: fix infinite directory reads for
offset dir") to prepare for a fix that can work properly on 32-bit
systems and might apply to recent LTS kernels where shmem employs
the simple_offset mechanism.

The Linux kernel CVE team has assigned CVE-2024-57952 to this issue.


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

	Issue introduced in 6.11 with commit 64a7ce76fb901bf9f9c36cf5d681328fc0fd4b5a and fixed in 6.12.12 with commit 9e9e710f68bac49bd9b587823c077d06363440e0
	Issue introduced in 6.11 with commit 64a7ce76fb901bf9f9c36cf5d681328fc0fd4b5a and fixed in 6.13.1 with commit 3f250b82040a72b0059ae00855a74d8570ad2147
	Issue introduced in 6.11 with commit 64a7ce76fb901bf9f9c36cf5d681328fc0fd4b5a and fixed in 6.14 with commit b662d858131da9a8a14e68661656989b14dbf113
	Issue introduced in 6.10.7 with commit 308b4fc2403b335894592ee9dc212a5e58bb309f

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-2024-57952
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/libfs.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/9e9e710f68bac49bd9b587823c077d06363440e0
	https://git.kernel.org/stable/c/3f250b82040a72b0059ae00855a74d8570ad2147
	https://git.kernel.org/stable/c/b662d858131da9a8a14e68661656989b14dbf113