CVE-2026-68235: drm/amd/display: dce100: skip non-DP stream encoders for DP MST

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

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

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

drm/amd/display: dce100: skip non-DP stream encoders for DP MST

On DCE8-class ASICs (e.g. Bonaire), the resource pool contains digital
DIG stream encoders plus one analog DAC encoder. When assigning a stream
encoder for a second DisplayPort MST stream, if the preferred digital
encoder is already acquired, dce100_find_first_free_match_stream_enc_for_link()
falls back to the first free pool entry. That entry may be the analog
encoder, whose funcs table lacks DP hooks such as dp_set_stream_attribute.
The subsequent atomic commit then dereferences NULL function pointers in
link_set_dpms_on() and crashes.

Skip encoders without dp_set_stream_attribute when the stream uses a DP
signal (including MST). Use dc_is_dp_signal(stream->signal) for the MST
fallback path instead of checking only the link connector signal.

Tested on:
- GPU: AMD Radeon R7 260X (Bonaire / DCE8)
- Board: Supermicro C9X299-PG300
- Setup: DP MST daisy chain, hotplug second monitor or have it connected on boot
- Kernel: 7.1.3 (issue observed since 6.19)
- Result: kernel oops without patch; dual monitors stable with patch

(cherry picked from commit 28ec64943e3ee4d9b8d30cea61e380f1429953a8)

The Linux kernel CVE team has assigned CVE-2026-68235 to this issue.


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

	Fixed in 6.12.101 with commit bfe28ce019c2d667d98071262da33d8bba122919
	Fixed in 6.18.42 with commit 51ea665c30c424c98959101f3bf6f48ab42949c8
	Fixed in 7.1.6 with commit ed2d86aef9fa4c43f82da0fca91a60f7326d7d03
	Fixed in 7.2-rc4 with commit d340cba0df4cf327c7e89c7c1a4e79d4771d7dd5

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-2026-68235
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/amd/display/dc/resource/dce100/dce100_resource.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/bfe28ce019c2d667d98071262da33d8bba122919
	https://git.kernel.org/stable/c/51ea665c30c424c98959101f3bf6f48ab42949c8
	https://git.kernel.org/stable/c/ed2d86aef9fa4c43f82da0fca91a60f7326d7d03
	https://git.kernel.org/stable/c/d340cba0df4cf327c7e89c7c1a4e79d4771d7dd5