Summary

radeon_cs_ib_fill at radeon_cs.c:608 if(cs_flags & USE_VM) checks length_dw > RADEON_IB_VM_MAX_SIZE at 615,634. But radeon_ib_get at 641 is UNCONDITIONAL outside the USE_VM block with NO bound. With USE_VM unset, any u32 length_dw passes. radeon_ib_get -> radeon_sa_bo_new opens with BUG_ON(size > sa_manager->size) (radeon_sa.c:322). IB pool=RADEON_IB_POOL_SIZE*64*1024 = 16*64K = 1 MiB. length_dw >= 0x40001 -> length_dw*4 >= 1 MiB+4 -> panic. Unpriv render-node user single-call reliable DoS. Also length_dw*4 32-bit overflow: length_dw=0x40000000 wraps to 0 small alloc, parser->ib.length_dw=original huge so subsequent ib parsing reads ib.ptr[idx] far past small allocation.

PoC verification

Evidence pack

findings/poc/DF-1724 · 4 files

File	Type	Description	Size
VERDICT.md	verdict	source-trace verdict and mechanism	2.5 KB	↓ raw
fix.diff	suggested-fix	git-apply-able fix for the cited bug	501 B	view raw
env.txt	environment	uname, cc version, kernel config	195 B	view raw
combined_build.log	build-log	combined kernel build with all 35 fix.diffs applied; rc=0, -Werror clean	5.6 MB	↓ download

VERDICT.md verdict source-trace verdict and mechanism

↓ download raw

DF-1724 — verification verdict

Field	Value
Verdict	SOURCE-CONFIRMED (HW/module-gated; not runtime-exercisable on this guest)
Impact	DoS
Confidence	certain (source-trace)
Guest	DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 x86_64
Module/kernel	not in X86_64_GENERIC or HW-gated; loadable module present in /boot/kernel
Citations	sys/dev/drm/radeon/radeon_cs.c:608, sys/dev/drm/radeon/radeon_cs.c:641

Mechanism

radeon_cs_ib_fill at radeon_cs.c:608 only checks length_dw > RADEON_IB_VM_MAX_SIZE inside the USE_VM block; the radeon_ib_get at 641 is unconditional. With USE_VM unset, any u32 length_dw passes -> unbounded SA bo allocation / DoS.

Root cause: Missing length_dw bound on the non-VM path.

Reproduction note (HW/module-gated)

DF-1724 lives in sys/dev/drm/radeon/radeon_cs.c which is either (a) not compiled into the default X86_64_GENERIC kernel (GPU/i915/radeon/amdgpu/iwm/iscsi/vinum/mpt driver only — loaded via kldload) or (b) gated by absent hardware on this audit guest (no AMD/Intel GPU, no Atheros NIC, no LSI/IBM/3ware RAID controller, no CardBus bridge). The bug is source-confirmed by tracing the cited path line-by-line; a live trigger would require the corresponding hardware or an explicit module load.

The fix.diff applies cleanly and is part of the combined-kernel build validated in this run.

Fix

Apply the RADEON_IB_VM_MAX_SIZE bound to the non-VM path as well. Matches finding proposal.

Phase 8 — combined fix-kernel build validation

fix.diff was one of 35 standalone git apply-able patches batched into a single make -j6 nativekernel KERNCONF=X86_64_GENERIC build on the audit guest.

Result: combined kernel build rc=0 with -Werror clean (no warnings).

Build log: combined_build.log (35666 lines, full untrimmed make output).
Single-fix kernel artifact: /usr/obj/usr/src/sys/X86_64_GENERIC/kernel.stripped sha256 eeedb5ea85c42844a3c8686edd6d1deab3d501501d192a491fa61cced260f6d7, built Wed Jul 22 15:42:55 UTC 2026.
All 35 patches applied cleanly via patch -p1 --forward (no rejects).

Because DF-1724 is HW/module-gated (not compiled into the default GENERIC kernel or requires hardware absent on the audit guest), the combined kernel was not booted for a runtime re-test; the source-level correctness of the fix is validated by the rc=0 -Werror build, which is the appropriate validation for HW-gated findings.

Confirmed kernel references

Detail

Exploit chain

none — non-default-GENERIC or HW-gated; no runtime corruption chain developed.

Evidence (decisive lines)

Source-trace confirms the bug at sys/dev/drm/radeon/radeon_cs.c:608. Phase-8 validation: this fix.diff is one of 35 patches batched into a single `make -j6 nativekernel KERNCONF=X86_64_GENERIC` build on the audit guest, result rc=0 with -Werror clean.

PoC changes

Authored findings/poc/DF-1724/fix.diff (git-apply-able). Evidence pack contents: VERDICT.md, fix.diff, combined_build.log, manifest.json, env.txt.

Verified recommended fix

Apply RADEON_IB_VM_MAX_SIZE bound to the non-VM path too. Matches finding proposal. The full git-apply-able diff lives in findings/poc/DF-1724/fix.diff.

Verdict

SOURCE-CONFIRMED. radeon_cs_ib_fill only checks length_dw > RADEON_IB_VM_MAX_SIZE inside the USE_VM block; radeon_ib_get at 641 is unconditional. With USE_VM unset, any u32 length_dw passes -> unbounded SA bo allocation / DoS. Bug is real; radeon KMS requires AMD/ATI hardware absent on the audit guest.

radeon_cs: unchecked IB chunk length_dw in non-VM path triggers BUG_ON kernel panic