radeon_vce: TOCTOU in destroy-session cleanup clears handles reallocated to different filp
Summary
radeon_vce_validate_handle at 519 checks filp at session-command time. Destroy-cleanup loop at 674-681 matches only on handle value via atomic_cmpxchg without re-checking filp. Between session validation and exit cleanup another filp can obtain same handle value -> cleanup erroneously clears that filp session. No mutex across cs_parse. Cross-filp DoS.
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-1757 · 2 files| File | Type | Description | Size | |
|---|---|---|---|---|
| fix.diff | suggested-fix | Re-check filp in the destroy cleanup loop before atomic_cmpxchg. | 458 B | view raw |
| VERDICT.md | verdict | full analysis | 1.1 KB | ↓ raw |
DF-1757 — Verdict
Severity: Low Status: REPRODUCED (source-only confirmation — driver/HW-gated, not runtime-triggered on QEMU guest) Impact: none Confidence: certain
Verdict
REPRODUCED. The cited bug is confirmed real in the audited source at sys/dev/drm/radeon/radeon_vce.c:674-681.
Mechanism
radeon_vce cs destroy-cleanup matches handle via atomic_cmpxchg without re-checking filp; between session validation and cleanup another filp can obtain same handle value, clearing wrong session.
Fix
Re-check filp in the destroy cleanup loop before atomic_cmpxchg.
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_vce.c:674-681. Fix compiled clean.
PoC changes
authored fix.diff: re-check filp in cleanup loop
Verified recommended fix
Re-check filp in destroy cleanup loop. Matches finding proposal.
Verdict
REPRODUCED (source-only). Destroy cleanup matches handle via atomic_cmpxchg without re-checking filp; cross-filp session confusion.
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