linux-cve-announce - CVE-2022-49699: filemap: Handle sibling entries in filemap_get_read

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Message-ID: <2025022628-CVE-2022-49699-d60e@gregkh>
Date: Wed, 26 Feb 2025 03:24:22 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2022-49699: filemap: Handle sibling entries in filemap_get_read_batch()

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

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

filemap: Handle sibling entries in filemap_get_read_batch()

If a read races with an invalidation followed by another read, it is
possible for a folio to be replaced with a higher-order folio.  If that
happens, we'll see a sibling entry for the new folio in the next iteration
of the loop.  This manifests as a NULL pointer dereference while holding
the RCU read lock.

Handle this by simply returning.  The next call will find the new folio
and handle it correctly.  The other ways of handling this rare race are
more complex and it's just not worth it.

The Linux kernel CVE team has assigned CVE-2022-49699 to this issue.


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

	Issue introduced in 5.12 with commit cbd59c48ae2bcadc4a7599c29cf32fd3f9b78251 and fixed in 5.18.8 with commit a66f131d30e53000f08301776bf85c912ef47aad
	Issue introduced in 5.12 with commit cbd59c48ae2bcadc4a7599c29cf32fd3f9b78251 and fixed in 5.19 with commit cb995f4eeba9d268fd4b56c2423ad6c1d1ea1b82

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-2022-49699
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/a66f131d30e53000f08301776bf85c912ef47aad
	https://git.kernel.org/stable/c/cb995f4eeba9d268fd4b56c2423ad6c1d1ea1b82