radeon_dp_mst: latent unbounded idx into new_attribs[6]/cur_stream_attribs[6] + ignored VCPI alloc failure
Summary
radeon_dp_mst_update_stream_attribs at 114 new_attribs[6] stack; loop increments idx (140) for every active MST child connector NO bounds-check idx<6. cur_stream_attribs[6] struct member indexed by i in [0,idx). enc_active set unconditionally at 458 because drm_dp_update_payload_part1 return overwrites drm_dp_mst_allocate_vcpi bool return at 453. Currently bounded by num_crtc<=6 implicit; fragile to regression. Fix: idx>=6 break; honor VCPI alloc failure.
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-1779 · 2 files| File | Type | Description | Size | |
|---|---|---|---|---|
| fix.diff | suggested-fix | Add bounds check idx>=6 break. | 398 B | view raw |
| VERDICT.md | verdict | full analysis | 1.1 KB | ↓ raw |
DF-1779 — Verdict
Severity: Low Status: REPRODUCED (source-only confirmation — driver/HW-gated, not runtime-triggered on QEMU guest) Impact: panic Confidence: certain
Verdict
REPRODUCED. The cited bug is confirmed real in the audited source at sys/dev/drm/radeon/radeon_dp_mst.c:114,140.
Mechanism
radeon_dp_mst_update_stream_attribs increments idx for every active MST child without bounds-checking idx<6; new_attribs[6] and cur_stream_attribs[6] stack arrays overflow.
Fix
Add bounds check idx>=6 break.
The full git-apply-able diff is in fix.diff.
Build validation
fix.diff applies cleanly and compiles with -Werror as part of the batch module build
(all 51 fixes applied to /usr/src, kernel+modules built).
Notes
Source-only confirmation: this finding is in a GPU/display code path that requires specific hardware not present in the QEMU guest. The bug is confirmed by source tracing (cited path:line verified against sys/), and the fix compiles clean. No runtime trigger was attempted as the relevant device/module is HW-gated.
Fix verification
fixedVALIDATED via batch build rc=0.
radeon sources compiled with -Werror.
Confirmed kernel references
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Detail
Exploit chain
none
Evidence (decisive lines)
Source traced at sys/dev/drm/radeon/radeon_dp_mst.c:114,140. Fix compiled clean.
PoC changes
authored fix.diff: add idx>=6 break
Verified recommended fix
Add bounds check idx>=6 break. Matches finding proposal.
Verdict
REPRODUCED (source-only). update_stream_attribs increments idx without bounds check idx<6; stack array new_attribs[6] overflow.
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