CVE-2026-68277: drm/dp/mst: fix OOB reads on 2-byte fields in 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 on 2-byte fields in sideband reply parsers

Three sideband reply parsers read 16-bit fields as:

  val = (raw->msg[idx] << 8) | (raw->msg[idx+1]);

and check bounds only after the fact. When idx == raw->curlen,
raw->msg[idx+1] reads one byte past the received message data into
the following struct fields (curchunk_len, curchunk_idx, curlen).

Affected functions:
 - drm_dp_sideband_parse_enum_path_resources_ack()
   full_payload_bw_number and avail_payload_bw_number fields
 - drm_dp_sideband_parse_allocate_payload_ack()
   allocated_pbn field
 - drm_dp_sideband_parse_query_payload_ack()
   allocated_pbn field

Fix by using a single combined check (idx + 2 > curlen) before each
2-byte read. Since the check is strictly tighter than idx > curlen,
no separate step is needed.

[added fixes tag]

The Linux kernel CVE team has assigned CVE-2026-68277 to this issue.


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

	Issue introduced in 3.17 with commit ad7f8a1f9ced7f049f9b66d588723f243a7034cd and fixed in 6.6.148 with commit bdf0508b1e6785d4a8982c637e97e68d60b47d7b
	Issue introduced in 3.17 with commit ad7f8a1f9ced7f049f9b66d588723f243a7034cd and fixed in 6.12.101 with commit 0bcd7675c69a2462a8531fcd9e4d096e9c7ec5df
	Issue introduced in 3.17 with commit ad7f8a1f9ced7f049f9b66d588723f243a7034cd and fixed in 6.18.42 with commit d5c70523cafa26ad2c7a37b612849abe2683baa8
	Issue introduced in 3.17 with commit ad7f8a1f9ced7f049f9b66d588723f243a7034cd and fixed in 7.1.6 with commit 68a624416d1dd481b3e5b7ea0e8a070a9b8a2c73
	Issue introduced in 3.17 with commit ad7f8a1f9ced7f049f9b66d588723f243a7034cd and fixed in 7.2-rc1 with commit 6b89ba3dba2f583626fb693e47e951ffb8bf591f

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-2026-68277
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/bdf0508b1e6785d4a8982c637e97e68d60b47d7b
	https://git.kernel.org/stable/c/0bcd7675c69a2462a8531fcd9e4d096e9c7ec5df
	https://git.kernel.org/stable/c/d5c70523cafa26ad2c7a37b612849abe2683baa8
	https://git.kernel.org/stable/c/68a624416d1dd481b3e5b7ea0e8a070a9b8a2c73
	https://git.kernel.org/stable/c/6b89ba3dba2f583626fb693e47e951ffb8bf591f