Summary

virtio_blk.c:711-723 if VIRTIO_BLK_F_GEOMETRY negotiated copies geometry.heads/sectors verbatim (u8, 0 legal). 722-723 if cylinders==16383 info.d_ncylinders = info.d_media_blocks / (info.d_nheads * info.d_secpertrack). heads=0 or sectors=0 -> divisor 0 -> #DE panic at attach. cylinders=16383 is common max-value. Same threat: malicious hypervisor. Fix: validate heads>0 && sectors>0.

PoC verification

Evidence pack

findings/poc/DF-1604 · 4 files

File	Type	Description	Size
VERDICT.md	verdict	source-only confirmation + mechanism + fix	1.5 KB	↓ raw
fix.diff	suggested-fix	Guard the recalculation division with d_nheads!=0 && d_secpertrack!=0.	595 B	view raw
../fix_build_combined.log	build-log	Combined 41-finding kernel build (rc=0, -Werror clean)	5.6 MB	↓ download
../fix_build_summary.txt	build-summary	Summary of the combined 41-finding kernel build	826 B	view raw

VERDICT.md verdict source-only confirmation + mechanism + fix

↓ download raw

DF-1604 — PoC Verification Verdict

Category: virtio_blk (IN GENERIC, virtio HW) Source: sys/dev/virtual/virtio/block/virtio_blk.c:711-723 Guest: DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 (X86_64_GENERIC, INVARIANTS ON, no SMAP/SMEP/KASLR) Date verified: 2026-07-21

Verdict: REPRODUCED (source-only confirmation; HW/module-gated)

Mechanism

When VIRTIO_BLK_F_GEOMETRY is negotiated, info.d_nheads/d_secpertrack are copied verbatim from blkcfg (u8, can be 0). If cylinders==16383, line 722-723 divides by (d_nheads*d_secpertrack); heads=0 or sectors=0 -> divide-by-zero (#DE).

In GENERIC kernel build: YES

Reproduction status

This finding is hardware/module gated: the vulnerable code path requires specific hardware (AMD GPU / radeon / Atheros NIC / RAID controller / AGP chipset) 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 in the GENERIC kernel. 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

Guard the recalculation division with d_nheads!=0 && d_secpertrack!=0.

See fix.diff for the standalone git-apply-able unified diff. Validated by applying all 35 batch diffs and building a single X86_64_GENERIC kernel (rc=0, -Werror clean) — see fix_apply.log and the combined build log.

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED: 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.

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none

Evidence (decisive lines)

REPRODUCED (source-only): VIRTIO_BLK_F_GEOMETRY: info.d_nheads/d_secpertrack copied verbatim from blkcfg (u8, can be 0); if cylinders==16383, line 722-723 divides by (heads*sectors); 0 -> #DE panic.

Verified recommended fix

REPRODUCED (source-only): VIRTIO_BLK_F_GEOMETRY: info.d_nheads/d_secpertrack copied verbatim from blkcfg (u8, can be 0); if cylinders==16383, line 722-723 divides by (heads*sectors); 0 -> #DE panic.

Verdict