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Bug#1116643: Processed: [bts-link] source package src:linux

From	Salvatore Bonaccorso <carnil@debian.org>
Newsgroups	linux.debian.bugs.dist, linux.debian.kernel
Subject	Bug#1116643: Processed: [bts-link] source package src:linux
Date	2026-08-12 21:30 +0200
Message-ID	<NrmOd-axF0-3@gated-at.bofh.it> (permalink)
References	(1 earlier) <Npaet-9kIr-3@gated-at.bofh.it> <LAos9-1uRl-1@gated-at.bofh.it> <NpaHw-9l2s-29@gated-at.bofh.it> <LAos9-1uRl-1@gated-at.bofh.it> <NpaHw-9l2s-29@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Cross-posted to 2 groups.

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Hi,

On Thu, Aug 06, 2026 at 07:58:38PM +0200, Vincent Lefevre wrote:
> On 2026-08-06 17:37:10 +0000, Debian Bug Tracking System wrote:
> > Processing commands for control@bugs.debian.org:
> > > # remote status report for #1116643 (http://bugs.debian.org/1116643)
> > > # Bug title: UBSAN: shift-out-of-bounds in .../drivers/gpu/drm/display/drm_dp_mst_topology.c (shift exponent -1)
> > > #  * https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/6303
> > > #  * remote status changed: (?) -> closed
> > > #  * closed upstream
> > > tags 1116643 + fixed-upstream
> > Bug #1116643 [src:linux] UBSAN: shift-out-of-bounds in .../drivers/gpu/drm/display/drm_dp_mst_topology.c (shift exponent -1)
> > Added tag(s) fixed-upstream.
> 
> At https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/6303
> there is no indication that the bug was fixed upstream.
> 
> FYI, I got this error only 3 times:
> 
> 2025-09-15T13:17:55+02:00 qaa kernel: UBSAN: shift-out-of-bounds in /build/reproducible-path/linux-6.16.7/drivers/gpu/drm/display/drm_dp_mst_topology.c:4574:36
> 2025-09-15T13:17:55+02:00 qaa kernel: shift exponent -1 is negative
> 2025-09-15T13:17:55+02:00 qaa kernel: CPU: 9 UID: 0 PID: 41777 Comm: kworker/u64:1 Not tainted 6.16.7+deb14-amd64 #1 PREEMPT(lazy)  Debian 6.16.7-1
> 
> 2025-09-29T10:01:20+02:00 qaa kernel: UBSAN: shift-out-of-bounds in /build/reproducible-path/linux-6.16.8/drivers/gpu/drm/display/drm_dp_mst_topology.c:4574:36
> 2025-09-29T10:01:20+02:00 qaa kernel: shift exponent -1 is negative
> 2025-09-29T10:01:20+02:00 qaa kernel: CPU: 4 UID: 0 PID: 490795 Comm: Xorg Not tainted 6.16.8+deb14-amd64 #1 PREEMPT(lazy)  Debian 6.16.8-1
> 
> 2025-12-02T09:56:26+01:00 qaa kernel: UBSAN: shift-out-of-bounds in /build/reproducible-path/linux-6.17.9/drivers/gpu/drm/display/drm_dp_mst_topology.c:4575:36
> 2025-12-02T09:56:26+01:00 qaa kernel: shift exponent -1 is negative
> 2025-12-02T09:56:26+01:00 qaa kernel: CPU: 4 UID: 0 PID: 34480 Comm: Xorg Not tainted 6.17.9+deb14-amd64 #1 PREEMPT(lazy)  Debian 6.17.9-1

The fix upstream would be:

v7.0-rc1: 342ccffd9f77fc29fe1c05fd145e4d842bd2feaa drm/display/dp_mst: Add protection against 0 vcpi

which got backported in turn as well to

v6.1.165: 95dbd525efce2a9e9e1c50ad15213de644c85ad0 drm/display/dp_mst: Add protection against 0 vcpi
v6.6.128: ac9a7c329a5610051fc476644c9b9145a5965ecb drm/display/dp_mst: Add protection against 0 vcpi
v6.12.75: 3f44cdb5371faf225af37d5caba8f21ec0572469 drm/display/dp_mst: Add protection against 0 vcpi
v6.18.16: 4d2ccdea18b564e3f73e3e543854acea64e6277d drm/display/dp_mst: Add protection against 0 vcpi

(but that is less relevant for this bug, if you are running unstable
kernel, so moving to the last kernel in unstable includes the above).

Regards,
Salvatore

Thread

Bug#1116643: Processed: [bts-link] source package src:linux Vincent Lefevre <vincent@vinc17.net> - 2026-08-06 20:10 +0200
  Bug#1116643: Processed: [bts-link] source package src:linux Vincent Lefevre <vincent@vinc17.net> - 2026-08-06 20:10 +0200
  Bug#1116643: Processed: [bts-link] source package src:linux Salvatore Bonaccorso <carnil@debian.org> - 2026-08-12 21:30 +0200
    Bug#1116643: Processed: [bts-link] source package src:linux Vincent Lefevre <vincent@vinc17.net> - 2026-08-13 13:10 +0200

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