Subject: CVE-2024-26630: mm: cachestat: fix folio read-after-free in cache walk

From: Greg Kroah-Hartman <[email-masked]>

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

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

mm: cachestat: fix folio read-after-free in cache walk

In cachestat, we access the folio from the page cache's xarray to compute
its page offset, and check for its dirty and writeback flags.  However, we
do not hold a reference to the folio before performing these actions,
which means the folio can concurrently be released and reused as another
folio/page/slab.

Get around this altogether by just using xarray's existing machinery for
the folio page offsets and dirty/writeback states.

This changes behavior for tmpfs files to now always report zeroes in their
dirty and writeback counters.  This is okay as tmpfs doesn't follow
conventional writeback cache behavior: its pages get "cleaned" during
swapout, after which they're no longer resident etc.

The Linux kernel CVE team has assigned CVE-2024-26630 to this issue.

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

	Issue introduced in 6.5 with commit cf264e1329fb and fixed in 6.6.21 with commit ba60fdf75e89
	Issue introduced in 6.5 with commit cf264e1329fb and fixed in 6.7.9 with commit fe7e008e0ce7
	Issue introduced in 6.5 with commit cf264e1329fb and fixed in 6.8 with commit 3a75cb05d53f

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-2024-26630
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:
	mm/filemap.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/ba60fdf75e89ea762bb617be578dc47f27655117
	https://git.kernel.org/stable/c/fe7e008e0ce728252e4ec652cceebcc62211657c
	https://git.kernel.org/stable/c/3a75cb05d53f4a6823a32deb078de1366954a804