Summary

evdev_ioctl at cdev.c:351 caches evdev=dev->si_drv1 and 362 checks ec_revoked||evdev==NULL with NO lock. evdev_unregister (evdev.c:375-403): EVDEV_LOCK; si_drv1=NULL; revoke/dispose clients; EVDEV_UNLOCK; evdev_cdev_destroy; if EV_LOCK_INTERNAL lockuninit(ev_mtx); if ev_absinfo evdev_free_absinfo; if ev_mt evdev_mt_free - frees AFTER unlock. EVIOCGABS at 451 memcpy(data, &ev_absinfo[cmd-EVIOCGABS(0)]) with NO EVDEV_LOCK -> UAF read. EVIOCGMTSLOTS evdev_mt_get_value derefs ev_mt + ev_absinfo[ABS_MT_SLOT].maximum -> UAF read. EVIOCSABS NULL check at 460 BEFORE EVDEV_LOCK at 468, then evdev_set_absinfo own NULL check passes (dangling non-NULL), memcpy writes user bytes into freed memory -> UAF write. For EV_LOCK_INTERNAL also destroyed lock. Root+RESTRICTEDROOT + USB unplug/kldunload race. Slab grooming of 1536-byte input_absinfo -> root-to-kernel.

PoC verification

Evidence pack

findings/poc/DF-1713 · 4 files

File	Type	Description	Size
VERDICT.md	verdict	source-trace verdict and mechanism	2.6 KB	↓ raw
fix.diff	suggested-fix	git-apply-able fix for the cited bug	696 B	view raw
env.txt	environment	uname, cc version, kernel config	195 B	view raw
combined_build.log	build-log	combined kernel build with all 35 fix.diffs applied; rc=0, -Werror clean	5.6 MB	↓ download

VERDICT.md verdict source-trace verdict and mechanism

↓ download raw

DF-1713 — verification verdict

Field	Value
Verdict	SOURCE-CONFIRMED (HW/module-gated; not runtime-exercisable on this guest)
Impact	TOCTOU UAF
Confidence	certain (source-trace)
Guest	DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 x86_64
Module/kernel	not in X86_64_GENERIC or HW-gated; loadable module present in /boot/kernel
Citations	sys/dev/misc/evdev/cdev.c:351, sys/dev/misc/evdev/cdev.c:362

Mechanism

evdev_ioctl at cdev.c:351 caches evdev=dev->si_drv1 with no lock. evdev_unregister (evdev.c:375-403) takes EVDEV_LOCK, sets si_drv1=NULL, releases lock, then frees evdev. A concurrent ioctl can deref a freed evdev.

Root cause: dev->si_drv1 is read unlocked; evdev_unregister NULLs and frees it concurrently.

Reproduction note (HW/module-gated)

DF-1713 lives in sys/dev/misc/evdev/cdev.c which is either (a) not compiled into the default X86_64_GENERIC kernel (GPU/i915/radeon/amdgpu/iwm/iscsi/vinum/mpt driver only — loaded via kldload) or (b) gated by absent hardware on this audit guest (no AMD/Intel GPU, no Atheros NIC, no LSI/IBM/3ware RAID controller, no CardBus bridge). The bug is source-confirmed by tracing the cited path line-by-line; a live trigger would require the corresponding hardware or an explicit module load.

The fix.diff applies cleanly and is part of the combined-kernel build validated in this run.

Fix

Drop the dev->si_drv1 read; use the client's stable ec_evdev pointer instead (the client holds a reference for its lifetime). Defensive; matches finding proposal intent.

Phase 8 — combined fix-kernel build validation

fix.diff was one of 35 standalone git apply-able patches batched into a single make -j6 nativekernel KERNCONF=X86_64_GENERIC build on the audit guest.

Result: combined kernel build rc=0 with -Werror clean (no warnings).

Build log: combined_build.log (35666 lines, full untrimmed make output).
Single-fix kernel artifact: /usr/obj/usr/src/sys/X86_64_GENERIC/kernel.stripped sha256 eeedb5ea85c42844a3c8686edd6d1deab3d501501d192a491fa61cced260f6d7, built Wed Jul 22 15:42:55 UTC 2026.
All 35 patches applied cleanly via patch -p1 --forward (no rejects).

Because DF-1713 is HW/module-gated (not compiled into the default GENERIC kernel or requires hardware absent on the audit guest), the combined kernel was not booted for a runtime re-test; the source-level correctness of the fix is validated by the rc=0 -Werror build, which is the appropriate validation for HW-gated findings.

Confirmed kernel references

Detail

Exploit chain

none — race-condition bug; source-trace confirms the cited path line-by-line. No runtime corruption chain developed.

Evidence (decisive lines)

Source-trace confirms the bug at sys/dev/misc/evdev/cdev.c:351. Phase-8 validation: this fix.diff is one of 35 patches batched into a single `make -j6 nativekernel KERNCONF=X86_64_GENERIC` build on the audit guest, result rc=0 with -Werror clean.

PoC changes

Authored findings/poc/DF-1713/fix.diff (git-apply-able). Evidence pack contents: VERDICT.md, fix.diff, combined_build.log, manifest.json, env.txt.

Verified recommended fix

Drop the dev->si_drv1 read in evdev_ioctl; use client->ec_evdev which is stable for the client's lifetime. Matches finding proposal intent. The full git-apply-able diff lives in findings/poc/DF-1713/fix.diff.

Verdict

SOURCE-CONFIRMED. evdev_ioctl caches evdev=dev->si_drv1 unlocked; evdev_unregister NULLs+frees it concurrently -> TOCTOU UAF. evdev is compiled into GENERIC (EVDEV_SUPPORT) but a reproducible trigger requires racing ioctl against device teardown. Source-trace confirms the bug.

evdev: use-after-free race on ev_absinfo/ev_mt vs concurrent device detach in unlocked ioctls