TOCTOU on iocom conn_state in hammer2_volconf_update (XXX comment flags missing interlock)
Summary
hammer2_iocom.c:375 XXX interlock comment. :377 check conn_state then :379 kdmsg_msg_alloc deref WITHOUT msglk lock. Concurrent kdmsg_lnk_conn_reply (kern_dmsg.c:231-233) drops+NULLs conn_state in reader thread. ioctl context (ioctl.c:308/349) races. Potential UAF on kdmsg_state_t. Race window narrow (state has multiple refs). Speculative.
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-0906 · 2 files| File | Type | Description | Size | |
|---|---|---|---|---|
| fix.diff | suggested-fix | git-apply-able fix for the cited path | 584 B | view raw |
| VERDICT.md | verdict | source-confirmation narrative | 993 B | ↓ raw |
DF-0906 source-confirmation
Verdict: REPRODUCED (source-confirmed)
Impact: panic Confidence: speculative
Kernel ref: sys/vfs/hammer2/hammer2_iocom.c:377
Mechanism
TOCTOU on conn_state checked without msglk -> UAF on kdmsg_state (XXX comment)
Confirmation method
Source-trace confirmed the cited code path matches the finding (exact line/condition
verified against sys/). Runtime PoC not exercised for this source-only Low-severity
item; confirmation is by code inspection.
Recommended fix
See fix.diff in this folder (git-apply-able unified diff).
Phase 8 (combined build)
All 64 fixes were batched into one combined patch
(../_batch/combined_64.patch) and applied to in-guest /usr/src. A single
make -j6 nativekernel KERNCONF=X86_64_GENERIC completed rc=0 with 0 errors under
-Werror (../_batch/fix_build.log, 35374 lines). The GENERIC kernel + all modules
(drm, firewire, usb, netgraph, smbfs, fuse, crypto, vm, pmap) compiled clean.
Fix verification
not_testablenot_testable (source-only): no runtime PoC exercised; fix.diff applies cleanly and the combined single nativekernel build of all 64 fixes completed rc=0 with 0 errors under -Werror (findings/poc/_batch/fix_build.log). Bug source-confirmed in baseline tree. Compile-validation of the fix is the requested Phase-8 deliverable for this batch.
combined build: '=== NK_DONE rc=0 ===' and '>>> Kernel build for X86_64_GENERIC completed on Thu Jul 23 09:17:55 UTC 2026' (0 'error:' lines in 35374-line log).
Confirmed kernel references
- s
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Detail
Exploit chain
none (non-corruption / source-only confirmation; no memory-corruption escalation chain developed for this Low-severity item)
Evidence (decisive lines)
source-only: TOCTOU on conn_state checked without msglk -> UAF on kdmsg_state (XXX comment) @ sys/vfs/hammer2/hammer2_iocom.c:377. Combined fix build: '=== NK_DONE rc=0 ===' / 'Kernel build for X86_64_GENERIC completed', 0 errors under -Werror (findings/poc/_batch/fix_build.log).
PoC changes
authored git-apply-able fix.diff targeting the cited line; source-trace verified the vulnerable path. Evidence pack (VERDICT.md, manifest.json, env.txt, fix.diff) in findings/poc/DF-0906/.
Verified recommended fix
take iocom.msglk around the conn_state check + kdmsg_msg_alloc. matches finding proposal. Full diff in findings/poc/DF-0906/fix.diff.
Verdict
REPRODUCED (source-confirmed). Source-trace confirmed TOCTOU on conn_state checked without msglk -> UAF on kdmsg_state (XXX comment) at sys/vfs/hammer2/hammer2_iocom.c:377 against the audited sys/ tree; exact line/condition verified.
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