CVE-2026-68279: drm/dp/mst: fix OOB reads in remote DPCD/I2C sideband reply parsers

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

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

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

drm/dp/mst: fix OOB reads in remote DPCD/I2C sideband reply parsers

drm_dp_sideband_parse_remote_dpcd_read() reads num_bytes from the raw
message and then unconditionally does:

  memcpy(bytes, &raw->msg[idx], num_bytes);

without checking that idx + num_bytes <= raw->curlen. raw->msg[] is
256 bytes; if a malicious or misbehaving MST hub sets num_bytes larger
than the remaining payload, the memcpy reads past the received data
into whatever follows in raw->msg[].

drm_dp_sideband_parse_remote_i2c_read_ack() has the same flaw (noted
with a /* TODO check */ comment since the code was introduced).

Fix both functions by using a single combined check
(idx + num_bytes > curlen) before each memcpy. Since num_bytes is u8,
it is always >= 0, so this strictly subsumes the simpler idx > curlen
form and no separate step is needed.

[added missing fixes tag]

The Linux kernel CVE team has assigned CVE-2026-68279 to this issue.


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

	Issue introduced in 3.17 with commit ad7f8a1f9ced7f049f9b66d588723f243a7034cd and fixed in 6.6.148 with commit 22d9f7fc1aaabaf73d5f30e8b0c9aa814ecd6ed2
	Issue introduced in 3.17 with commit ad7f8a1f9ced7f049f9b66d588723f243a7034cd and fixed in 6.12.101 with commit 04d953f50d61e542e94a5977822cc53735f8c0ce
	Issue introduced in 3.17 with commit ad7f8a1f9ced7f049f9b66d588723f243a7034cd and fixed in 6.18.42 with commit 533d9e2bede4aeefdc2a0561d7071cfede95958f
	Issue introduced in 3.17 with commit ad7f8a1f9ced7f049f9b66d588723f243a7034cd and fixed in 7.1.6 with commit e6ef5455b06cb4e5d181aabcd723791587c79f12
	Issue introduced in 3.17 with commit ad7f8a1f9ced7f049f9b66d588723f243a7034cd and fixed in 7.2-rc1 with commit 1a8f537f5a1eeac941f262fe73078d6b08ba83c0

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-2026-68279
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:
	drivers/gpu/drm/display/drm_dp_mst_topology.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/22d9f7fc1aaabaf73d5f30e8b0c9aa814ecd6ed2
	https://git.kernel.org/stable/c/04d953f50d61e542e94a5977822cc53735f8c0ce
	https://git.kernel.org/stable/c/533d9e2bede4aeefdc2a0561d7071cfede95958f
	https://git.kernel.org/stable/c/e6ef5455b06cb4e5d181aabcd723791587c79f12
	https://git.kernel.org/stable/c/1a8f537f5a1eeac941f262fe73078d6b08ba83c0