# DF-2409 VERDICT

**Status:** reproduced
**Impact:** panic
**Confidence:** certain

UAF write through the stale 500ms discard_buffer_callout: production tpm20_init created a real /dev/tpm0, a userland open+write+close armed the callout via production tpm20_write, production tpm20_release freed/uninited without draining it, the sc was freed and immediately resurrected at the same address with sc->buf = 0x4141414141414141, and the callout fired into the freed object: Fatal trap 9 general protection fault at tpm20_discard_buffer+0x3d (movq $0,(%rcx)) - the memset(sc->buf,...) store through the canary pointer.

## Kernel references
- `sys/dev/crypto/tpm/tpm20.c:144`
- `sys/dev/crypto/tpm/tpm20.c:199`
- `sys/dev/crypto/tpm/tpm20.c:213`

## Guest
DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul  2 06:02:54 UTC 2026 root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC x86_64

## Notes
trigger window: release/detach within 500ms of the write; root-only device (0600)

## 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.