DF-1605

NULL-pointer dereference in vtblk_strategy: sc dereferenced before the NULL check

Summary

virtio_blk.c:527 sc=dev->si_drv1. 529 q=&sc->vtblk_queues[sc->vtblk_vqmap[mycpuid]] DEREFS sc. 531 if (sc==NULL) DEAD CODE: deref already happened. Compare vtblk_open 467-473 and vtblk_dump 489-491 which check NULL first. Currently unreachable: si_drv1 never cleared in detach (set at 752, destroyed via disk_destroy at 408 without NULLing). Latent footgun: if future code clears si_drv1 during detach, NULL-deref panic. Fix: hoist NULL check above deref.

Discussion (0)

No comments yet.

Severity: Low
Status: new
Bucket: Base system — drivers
Confidence: likely
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U:C:N/I:N/A:L
CWE: CWE-476 NULL Pointer Dereference
File: sys/dev/virtual/virtio/block/virtio_blk.c
Lines: 527-533
Area: dev
Discovered: 2026-07-18
Updated: 2026-07-18

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: panic
Confidence: likely
Tested: 2026-07-23 17:00:07
Attempts: —
Runtime: —
Code hash: —
Guest: DragonFly dfbsd 6.5-DEVELOPMENT #0
Build cmd: —
Run cmd: —

jump to evidence pack ↓

Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: likely
Tested: 2026-07-23 17:00:07
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1605/fix.diff
Runner: df-bsd-pocrunner

jump to fix verification ↓

PoC verification

Evidence pack

findings/poc/DF-1605 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	598 B	view raw
VERDICT.md	verdict	source-confirmation analysis	721 B	↓ raw
build.sh	build-script	N/A (source-only)	61 B	view raw
run.sh	run-script	N/A (source-only)	87 B	view raw

VERDICT.md verdict source-confirmation analysis

↓ download raw

DF-1605 VERDICT

Verdict: REPRODUCED (source-confirmed)

Impact: Low (driver-level NULL deref / OOB / leak / DoS — hardware-gated)

Mechanism: virtio_blk.c:527 sc=dev->si_drv1. 529 q=&sc->vtblk_queues[sc->vtblk_vqmap[mycpuid]] DEREFS sc. 531 if (sc==NULL) DEAD CODE: deref already happened. Compare vtblk_open 467-473 and vtblk_dump 489-491 wh

Citation: sys/dev/virtual/virtio/block/virtio_blk.c:527-533

Fix: Applied fix.diff — compiles in batch kernel build (rc=0, -Werror).

Verification method: Source-only line-by-line trace of cited path:line. Low-severity driver bug; PoC trigger requires specific hardware or root context. Confirmed the cited vulnerable pattern exists in source.

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

fix.diff compiled in batch kernel build rc=0 -Werror

fix.diff compiled in batch kernel build rc=0 -Werror

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none (Low severity)

Evidence (decisive lines)

Source-confirmed: vtblk_strategy derefs sc before NULL check (virtio_blk.c:527-531)

Verified recommended fix

Source-confirmed: vtblk_strategy derefs sc before NULL check (virtio_blk.c:527-531)

Verdict

Source-confirmed: vtblk_strategy derefs sc before NULL check (virtio_blk.c:527-531)