CVE-2025-71305

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

drm/display/dp_mst: Add protection against 0 vcpi

When releasing a timeslot there is a slight chance we may end up

with the wrong payload mask due to overflow if the delayed_destroy_work

ends up coming into play after a DP 2.1 monitor gets disconnected

which causes vcpi to become 0 then we try to make the payload =

~BIT(vcpi - 1) which is a negative shift. VCPI id should never

really be 0 hence skip changing the payload mask if VCPI is 0.

Otherwise it leads to

<7> [515.287237] xe 0000:03:00.0: [drm:drm_dp_mst_get_port_malloc

[drm_display_helper]] port ffff888126ce9000 (3)

<4> [515.287267] -----------[ cut here ]-----------

<3> [515.287268] UBSAN: shift-out-of-bounds in

../drivers/gpu/drm/display/drm_dp_mst_topology.c:4575:36

<3> [515.287271] shift exponent -1 is negative

<4> [515.287275] CPU: 7 UID: 0 PID: 3108 Comm: kworker/u64:33 Tainted: G

S U 6.17.0-rc6-lgci-xe-xe-3795-3e79699fa1b216e92+ #1 PREEMPT(voluntary)

<4> [515.287279] Tainted: [S]=CPU_OUT_OF_SPEC, [U]=USER

<4> [515.287279] Hardware name: ASUS System Product Name/PRIME Z790-P

WIFI, BIOS 1645 03/15/2024

<4> [515.287281] Workqueue: drm_dp_mst_wq drm_dp_delayed_destroy_work

[drm_display_helper]

<4> [515.287303] Call Trace:

<4> [515.287304] <TASK>

<4> [515.287306] dump_stack_lvl+0xc1/0xf0

<4> [515.287313] dump_stack+0x10/0x20

<4> [515.287316] __ubsan_handle_shift_out_of_bounds+0x133/0x2e0

<4> [515.287324] ? drm_atomic_get_private_obj_state+0x186/0x1d0

<4> [515.287333] drm_dp_atomic_release_time_slots.cold+0x17/0x3d

[drm_display_helper]

<4> [515.287355] mst_connector_atomic_check+0x159/0x180 [xe]

<4> [515.287546] drm_atomic_helper_check_modeset+0x4d9/0xfa0

<4> [515.287550] ? __ww_mutex_lock.constprop.0+0x6f/0x1a60

<4> [515.287562] intel_atomic_check+0x119/0x2b80 [xe]

<4> [515.287740] ? find_held_lock+0x31/0x90

<4> [515.287747] ? lock_release+0xce/0x2a0

<4> [515.287754] drm_atomic_check_only+0x6a2/0xb40

<4> [515.287758] ? drm_atomic_add_affected_connectors+0x12b/0x140

<4> [515.287765] drm_atomic_commit+0x6e/0xf0

<4> [515.287766] ? _pfx__drm_printfn_info+0x10/0x10

<4> [515.287774] drm_client_modeset_commit_atomic+0x25c/0x2b0

<4> [515.287794] drm_client_modeset_commit_locked+0x60/0x1b0

<4> [515.287795] ? mutex_lock_nested+0x1b/0x30

<4> [515.287801] drm_client_modeset_commit+0x26/0x50

<4> [515.287804] __drm_fb_helper_restore_fbdev_mode_unlocked+0xdc/0x110

<4> [515.287810] drm_fb_helper_hotplug_event+0x120/0x140

<4> [515.287814] drm_fbdev_client_hotplug+0x28/0xd0

<4> [515.287819] drm_client_hotplug+0x6c/0xf0

<4> [515.287824] drm_client_dev_hotplug+0x9e/0xd0

<4> [515.287829] drm_kms_helper_hotplug_event+0x1a/0x30

<4> [515.287834] drm_dp_delayed_destroy_work+0x3df/0x410

[drm_display_helper]

<4> [515.287861] process_one_work+0x22b/0x6f0

<4> [515.287874] worker_thread+0x1e8/0x3d0

<4> [515.287879] ? __pfx_worker_thread+0x10/0x10

<4> [515.287882] kthread+0x11c/0x250

<4> [515.287886] ? __pfx_kthread+0x10/0x10

<4> [515.287890] ret_from_fork+0x2d7/0x310

<4> [515.287894] ? __pfx_kthread+0x10/0x10

<4> [515.287897] ret_from_fork_asm+0x1a/0x30