CVE-2025-71305 — drm/display/dp_mst: Add protection against 0 vcpi

Affected: Linux

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+0x186/0x…

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CVE-2025-71305 — drm/display/dp_mst: Add protection against 0 vcpi