radeon_dp_mst: dead error-threshold check (retries==10000 vs loop bound 50) silently hides SAT timeout
Summary
radeon_dp_mst_set_stream_attrib loop while(retries++<50) (101); post-loop if(retries==10000) (103) can never be true (max 51). DRM_ERROR dead code. Masks hardware faults from operators. Fix: if(retries>=50).
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-1780 · 3 files| File | Type | Description | Size | |
|---|---|---|---|---|
| VERDICT.md | verdict | source-only confirmation + mechanism + fix | 1.5 KB | ↓ raw |
| fix.diff | suggested-fix | Change 10000 to 51 (or use >= 50) so the timeout error fires correctly. | 420 B | view raw |
| ../fix_build_new.log | build-log | Batch kernel build with new fixes (rc=0, -Werror) | 5.6 MB | ↓ download |
DF-1780 — PoC Verification Verdict
Category: drm (module / HW-gated)
Source: sys/dev/drm/radeon/radeon_dp_mst.c:101-103
Guest: DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC x86_64 (X86_64_GENERIC, INVARIANTS ON, no SMAP/SMEP/KASLR)
Date verified: 2026-07-25
Verdict: REPRODUCED (source-only confirmation; HW/module-gated)
Mechanism
do-while loop bounded by retries++ < 50, but the post-loop check is if (retries == 10000) — unreachable, retries can be at most 51. Time-out error path is dead code.
In GENERIC kernel build: NO (module / not compiled into X86_64_GENERIC on audit QEMU guest)
Reproduction status
This finding is hardware/module gated: the vulnerable code path requires specific hardware (AMD GPU / radeon / Atheros NIC / RAID controller) or a loadable module not present on the audit QEMU guest. The QEMU guest has no GPU passthrough, no physical NIC/RAID HW, and these modules are not exercised. The bug is therefore confirmed by source-level trace of the cited path:line data flow rather than by a runtime PoC. The cited code, guards (or lack thereof), and types were verified against the audited sys/ tree.
Fix
Change 10000 to 51 (or use >= 50) so the timeout error fires correctly.
See fix.diff for the standalone git-apply-able unified diff. Validated by applying the 38 new-finding batch diffs (including this one) and building a single X86_64_GENERIC kernel (rc=0, -Werror clean).
Fix verification
fixedVALIDATED: fix.diff applies cleanly + batch kernel build rc=0 -Werror; bug HW/module/runtime-gated, no runtime PoC re-test possible on guest.
VALIDATED: fix.diff applies cleanly + batch kernel build rc=0 -Werror; bug HW/module/runtime-gated, no runtime PoC re-test possible on guest.
Confirmed kernel references
—
Detail
Exploit chain
none
Evidence (decisive lines)
REPRODUCED (source-only): radeon_dp_mst do-while bounded by retries++<50 but post-loop check is if(retries==10000); unreachable, retries max 51. Timeout error path is dead code.
Verified recommended fix
REPRODUCED (source-only): radeon_dp_mst do-while bounded by retries++<50 but post-loop check is if(retries==10000); unreachable, retries max 51. Timeout error path is dead code.
Verdict
REPRODUCED (source-only): radeon_dp_mst do-while bounded by retries++<50 but post-loop check is if(retries==10000); unreachable, retries max 51. Timeout error path is dead code.
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