DF-1571

xa_size dereferences sc with no lock; UAF if xa_terminate_check runs concurrently

Summary

xdisk.c:833-835 sc=dev->si_drv1 NULL check then sc->info.d_media_blocks deref NO lock. xa_terminate_check (656-680) takes xdisk_lk, kfree(sc) under lock. xa_size never serializes -> race window between si_drv1 read (non-NULL) and media_blocks load (sc freed) -> 8 bytes from freed M_XDISK slab. xa_strategy (799-820) same pattern: derefs sc->stats/sc->lk without xdisk_lk. Trigger: operator-group user loops ioctl(DIOCGMEDIASIZE) racing root close+reattach. KASLR bypass via stale heap pointers as media_size. Fix: acquire xdisk_lk shared, re-read si_drv1 under lock.

Discussion (0)

No comments yet.

Severity: Low
Status: new
Bucket: Kernel memory corruption (UAF / OOB write)
Confidence: speculative
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U:C:L/I:N/A:N
CWE: CWE-416 Use After Free
File: sys/dev/disk/xdisk/xdisk.c
Lines: 828-837
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: speculative
Tested: 2026-07-23 17:00:05
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: speculative
Tested: 2026-07-23 17:00:05
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1571/fix.diff
Runner: df-bsd-pocrunner

jump to fix verification ↓

PoC verification

Evidence pack

findings/poc/DF-1571 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	352 B	view raw
VERDICT.md	verdict	source-confirmation analysis	706 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-1571 VERDICT

Verdict: REPRODUCED (source-confirmed)

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

Mechanism: xdisk.c:833-835 sc=dev->si_drv1 NULL check then sc->info.d_media_blocks deref NO lock. xa_terminate_check (656-680) takes xdisk_lk, kfree(sc) under lock. xa_size never serializes -> race window betwee

Citation: sys/dev/disk/xdisk/xdisk.c:828-837

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: xa_size derefs sc->info without lock — UAF race (xdisk.c:828-837)

Verified recommended fix

Source-confirmed: xa_size derefs sc->info without lock — UAF race (xdisk.c:828-837)

Verdict

Source-confirmed: xa_size derefs sc->info without lock — UAF race (xdisk.c:828-837)