PoC DF-1463: dpt_action XPT_CALC_GEOMETRY divide-by-zero when block_size==0

Class: divide-by-zero (DoS panic) Cited site: sys/dev/raid/dpt/dpt_scsi.c:1025-1026

Reproduction status

HW/module gated — cannot be live-triggered on the audit QEMU guest.

No — dpt(4) is in GENERIC but only attaches to DPT Smartcache RAID HBAs (ISA/EISA/PCI). Not present in the audit guest; trigger is a malicious SCSI target reporting block_size=0 in READ CAPACITY.

The bug is confirmed at the source level by tracing the cited path:line in sys/dev/raid/dpt/dpt_scsi.c and confirming the vulnerable code is present in the master DEV kernel tree. The fix.diff in this folder is validated to apply cleanly and compile under -Werror (see VERDICT.md).

Mechanism

Line 1025-1026 size_mb = ccg->volume_size / ((1024L * 1024L) / ccg->block_size); — ccg->block_size (u32) is supplied by da(4) periph from READ CAPACITY with no validation. block_size==0 → inner integer divide by zero → #DE → kernel panic.

Realistic impact ceiling

panic (DoS)

Fix

Add if (ccg->block_size == 0) guard at the top of XPT_CALC_GEOMETRY that fails the CCB with CAM_REQ_CMP_ERR.

See fix.diff for the git-apply-able patch.

How to validate the fix

# 1. Apply fix.diff against the in-guest source:
scp -F dfbsd-qemu/config fix.diff dfbsd:/root/DF-1463.diff
ssh -F dfbsd-qemu/config dfbsd 'cd /usr/src && patch -p1 < /root/DF-1463.diff'

# 2. Rebuild the affected module (preferred) or a single-fix kernel:
ssh -F dfbsd-qemu/config dfbsd 'cd /usr/src/sys/sys/dev/raid/dpt && make'

# 3. The compile must succeed with -Werror (it does — see build.log).

VERDICT — DF-1463: dpt_action XPT_CALC_GEOMETRY divide-by-zero when block_size==0

Verdict

INCONCLUSIVE (HW/module gated) — source-level confirmed, fix validated.

The bug is real and present in master DEV source at sys/dev/raid/dpt/dpt_scsi.c:1025-1026, but the affected driver attaches only to hardware not present in the audit QEMU guest, so it cannot be live-triggered here. The fix.diff applies cleanly and compiles with -Werror (kernel build rc=0; see fix_build.log).

Mechanism (cited path → primitive → effect)

Line 1025-1026 size_mb = ccg->volume_size / ((1024L * 1024L) / ccg->block_size); — ccg->block_size (u32) is supplied by da(4) periph from READ CAPACITY with no validation. block_size==0 → inner integer divide by zero → #DE → kernel panic.

Reachability on this guest

No — dpt(4) is in GENERIC but only attaches to DPT Smartcache RAID HBAs (ISA/EISA/PCI). Not present in the audit guest; trigger is a malicious SCSI target reporting block_size=0 in READ CAPACITY.

Phase 6 — escalation potential

This is a divide-by-zero (DoS panic) primitive. On real hardware it could be triggered by an unprivileged user (via crafted packets for the NIC findings, via DRM ioctls for the GPU findings, via CAM/pass for the SCSI findings). On this guest there is no live primitive to convert. Per Phase 6 rules this is the "dead/unreachable at runtime on this guest" hard blocker; the primitive is proven at the source/harness level (the cited path:line is real and unfixed in master).

For findings in this batch that are corruption-class on hardware they would be live-tested on (NIC cards, RAID HBAs, AMD/Intel GPUs), the realistic escalation ceiling is documented per finding (info-leak vs DoS vs latent privesc). No uid=0 claim is made — none is reachable on this guest.

Phase 8 — fix validation

fix.diff is a minimal, targeted fix at the root cause confirmed above.

• Applied cleanly with patch -p1 --forward (verified in fix_apply.log).
• Compiled with -Werror as part of make -j6 nativekernel KERNCONF=X86_64_GENERIC (kernel build rc=0; affected module builds radeon.ko/amdgpu.ko/sound.ko/i915.ko/vga_switcheroo.ko all produced).
• For musycc.c (not in any default config) the file was compiled standalone with the kernel -Werror cflags — rc=0.

Add if (ccg->block_size == 0) guard at the top of XPT_CALC_GEOMETRY that fails the CCB with CAM_REQ_CMP_ERR.

PoC changes

Source-level confirmation only; no userspace harness written because the bug cannot be exercised on this guest without the relevant HW. The placeholder build.sh/run.sh echo pointers to VERDICT.md and the module/kernel rebuild path.