Bug 2514439 (CVE-2026-68429)

Summary: CVE-2026-68429 kernel: drm/dp_mst: Handle torn-down topology gracefully in drm_dp_mst_topology_queue_probe()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's DisplayPort (DP) Multi-Stream Transport (MST) module. A race condition can occur during hotplug or link-loss events when the MST topology is being torn down while the `drm_dp_mst_topology_queue_probe()` function is called. This can lead to spurious kernel warnings and cause the display compositor to crash when connecting or disconnecting DP MST monitors, resulting in a denial of service.
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Description OSIDB Bzimport 2026-08-12 00:21:24 UTC 
In the Linux kernel, the following vulnerability has been resolved:

drm/dp_mst: Handle torn-down topology gracefully in drm_dp_mst_topology_queue_probe()

A hotplug or link-loss event can tear down the MST topology
(setting mgr->mst_state = false and mgr->mst_primary = NULL) concurrently
with a caller invoking drm_dp_mst_topology_queue_probe(). Since the check
is already performed under mgr->lock, the condition is not a programming
error but a valid race -- the topology was valid when the caller decided
to call this function, but was torn down before the lock was acquired.

Replace the drm_WARN_ON() with a graceful early return. This eliminates
spurious kernel warnings and the resulting compositor crashes observed
when connecting/disconnecting DP MST monitors, while keeping the correct
behavior of doing nothing when MST is not active. A drm_dbg_mst() trace
is added so the skipped probe remains observable under MST debug logging.

The existing WARN_ON(mgr->mst_primary) in drm_dp_mst_topology_mgr_set_mst()
already catches the case where the topology is initialized twice, so no
diagnostic coverage is lost.
Comment 1 Mauro Matteo Cascella 2026-08-12 15:56:29 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026081251-CVE-2026-68429-d0b9@gregkh/T