linux-cve-announce - CVE-2025-21777: ring-buffer: Validate the persistent meta data subbuf array

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Message-ID: <2025022607-CVE-2025-21777-0c96@gregkh>
Date: Wed, 26 Feb 2025 18:17:33 -0800
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21777: ring-buffer: Validate the persistent meta data subbuf array

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

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

ring-buffer: Validate the persistent meta data subbuf array

The meta data for a mapped ring buffer contains an array of indexes of all
the subbuffers. The first entry is the reader page, and the rest of the
entries lay out the order of the subbuffers in how the ring buffer link
list is to be created.

The validator currently makes sure that all the entries are within the
range of 0 and nr_subbufs. But it does not check if there are any
duplicates.

While working on the ring buffer, I corrupted this array, where I added
duplicates. The validator did not catch it and created the ring buffer
link list on top of it. Luckily, the corruption was only that the reader
page was also in the writer path and only presented corrupted data but did
not crash the kernel. But if there were duplicates in the writer side,
then it could corrupt the ring buffer link list and cause a crash.

Create a bitmask array with the size of the number of subbuffers. Then
clear it. When walking through the subbuf array checking to see if the
entries are within the range, test if its bit is already set in the
subbuf_mask. If it is, then there is duplicates and fail the validation.
If not, set the corresponding bit and continue.

The Linux kernel CVE team has assigned CVE-2025-21777 to this issue.

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

	Issue introduced in 6.12 with commit c76883f18e59b762247ee91d3e4224231711854e and fixed in 6.12.16 with commit 3ec743d558f111d8999aea24577ba66c65ee2eeb
	Issue introduced in 6.12 with commit c76883f18e59b762247ee91d3e4224231711854e and fixed in 6.13.4 with commit 0d547a6f5e8fad26ebc12f501d7d19fccdbad6bf
	Issue introduced in 6.12 with commit c76883f18e59b762247ee91d3e4224231711854e and fixed in 6.14-rc3 with commit f5b95f1fa2ef3a03f49eeec658ba97e721412b32

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-2025-21777
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:
	kernel/trace/ring_buffer.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/3ec743d558f111d8999aea24577ba66c65ee2eeb
	https://git.kernel.org/stable/c/0d547a6f5e8fad26ebc12f501d7d19fccdbad6bf
	https://git.kernel.org/stable/c/f5b95f1fa2ef3a03f49eeec658ba97e721412b32