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CVE-2025-40354
drm/amd/display: increase max link count and fix link->enc NULL pointer access
Published 2025-12-16 (10 months ago) by the Linux kernel CNA. Subsystem drivers/gpu. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2025-40354 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| Debian 13trixie | fixed | 6.12.57-1 | Update the kernel and reboot. Fixed in 6.12.57-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 6.17.6-1 | Update the kernel and reboot. Fixed in 6.17.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 6.17.6-1 | Update the kernel and reboot. Fixed in 6.17.6-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
[why] 1.) dc->links[MAX_LINKS] array size smaller than actual requested. max_connector + max_dpia + 4 virtual = 14. increase from 12 to 14. 2.) hw_init() access null LINK_ENC for dpia non display_endpoint. (cherry picked from commit d7f5a61e1b04ed87b008c8d327649d184dc5bb45)
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
drivers/gpu/drm/amd/display/dc/hwss/dcn401/dcn401_hwseq.c
drivers/gpu/drm/amd/display/dc/inc/hw/hw_shared.h
- What this is
- AMD DISPLAY COREMAINTAINERS section matched on drivers/gpu/drm/amd/display/ · amd-gfx@lists.freedesktop.org · Supported
Show whether Debian builds this, per release
Not established. This site could not find the build rule for the affected file in the kernel trees Debian ships, so it has no answer about whether Debian compiles this code. Read that as unknown, never as absent.
- bookworm, trixie, forky, sid?
- ?
- not established - no Makefile entry for the affected file
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS
Signals
- Published
- 2025-12-16 (10 months ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.15%, higher than 4.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/gpu
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.15 | 6.12.56 | f28092be4e12 |
| 4.15 | 6.17.6 | a3fc0d36cfb9 |
| 4.15 | 6.18 | bec947cbe9a6 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The defect is in the amdgpu DC display driver's hardware-init path, reached through local driver probe and suspend/resume (including runtime-PM resume driven by opening /dev/dri/renderD*). There is no network-facing component.
- AC:LAttack complexity, low
- Both the unbounded `dc->links[]` append in create_links() and the NULL `link->link_enc` dereference for DPIA endpoints are deterministic on affected DCN4x configurations — no race to win and no memory layout beyond the attacker's influence.
- PR:LPrivileges required, low
- The vulnerable init_hw path is re-entered on every runtime-PM/system resume via dm_resume() -> dc_set_power_state(D0), which an unprivileged local user holding an ordinary DRM/render node handle can drive repeatedly; no root or CAP_SYS_ADMIN is required.
- UI:NUser interaction, none
- No victim action is needed — the corrupting create_links() loop runs at driver init and the NULL dereference is hit automatically on each hardware init/resume cycle.
- S:UScope, unchanged
- The out-of-bounds write and NULL dereference stay within the kernel's own security authority; no VM, IOMMU, or sandbox boundary is crossed.
- C:HConfidentiality impact, high
- Overflowing dc->links[] overwrites the adjacent `struct link_service *link_srv`, `current_state`, and `res_pool` pointers in struct dc, so subsequent dc->link_srv->...() dispatches read from an attacker-influenceable heap object, yielding pointer confusion and arbitrary kernel-memory read primitives.
- I:HIntegrity impact, high
- This is an out-of-bounds write of pointer values past a fixed array directly onto a function-pointer-table pointer (link_srv), giving a realistic indirect-call hijack and arbitrary write path rather than a bounded corruption.
- A:HAvailability impact, high
- The unfixed DPIA path dereferences a NULL link->link_enc in dcn401_init_hw(), producing a kernel oops on every hardware init/resume, and the adjacent-field corruption reliably panics the machine.