Description

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

soc: qcom: pmic_glink_altmode: fix drm bridge use-after-free

A recent DRM series purporting to simplify support for "transparent
bridges" and handling of probe deferrals ironically exposed a
use-after-free issue on pmic_glink_altmode probe deferral.

This has manifested itself as the display subsystem occasionally failing
to initialise and NULL-pointer dereferences during boot of machines like
the Lenovo ThinkPad X13s.

Specifically, the dp-hpd bridge is currently registered before all
resources have been acquired which means that it can also be
deregistered on probe deferrals.

In the meantime there is a race window where the new aux bridge driver
(or PHY driver previously) may have looked up the dp-hpd bridge and
stored a (non-reference-counted) pointer to the bridge which is about to
be deallocated.

When the display controller is later initialised, this triggers a
use-after-free when attaching the bridges:

dp -> aux -> dp-hpd (freed)

which may, for example, result in the freed bridge failing to attach:

[drm:drm_bridge_attach [drm]] *ERROR* failed to attach bridge /soc@0/phy@88eb000 to encoder TMDS-31: -16

or a NULL-pointer dereference:

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
...
Call trace:
drm_bridge_attach+0x70/0x1a8 [drm]
drm_aux_bridge_attach+0x24/0x38 [aux_bridge]
drm_bridge_attach+0x80/0x1a8 [drm]
dp_bridge_init+0xa8/0x15c [msm]...

Classification

CVE ID: CVE-2024-26909

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.04% (probability of being exploited)

EPSS Percentile: 5.08% (scored less or equal to compared to others)

EPSS Date: 2025-02-04 (when was this score calculated)

References

https://git.kernel.org/stable/c/2bbd65c6ca567ed8dbbfc4fb945f57ce64bef342
https://git.kernel.org/stable/c/ef45aa2841e15b649e5417fe3d4de395fe462781
https://git.kernel.org/stable/c/b979f2d50a099f3402418d7ff5f26c3952fb08bb

Timeline