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.

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	1.0 KB	↓ raw
build.sh	build-script	N/A (source-only)	65 B	view raw
run.sh	run-script	N/A (source-only)	89 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 status (batch validation)

Applied with the 36 sibling fix.diffs of this batch in findings/poc/_batch41/all_fixes.patch; single in-guest make -j6 nativekernel KERNCONF=X86_64_GENERIC completed RC=0 with zero errors under -Werror (full log: findings/poc/_batch41/fix_build8.log). Behavior A/B intentionally skipped for this Info-tier item.

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