Memory leak of dios_io/dios_open on kdmsg state teardown (no destructor for state->any.any)
Summary
diskiodone eof path(:637-639) and disk_blk_open paths never kfree(iost/openst) on kdmsg teardown. kdmsg_state_free(kern_dmsg.c:1754-1764) has no destructor for state->any.any. Peer can repeat OPEN/READ-WITH-DELETE+abort cycles to exhaust M_DEVBUF.
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-0118 · 5 files| File | Type | Description | Size | |
|---|---|---|---|---|
| fix.diff | suggested-fix | git-apply-able unified diff | 586 B | view raw |
| VERDICT.md | verdict | source-trace and fix validation | 1.2 KB | ↓ raw |
| README.md | readme | reproduce instructions | 785 B | ↓ raw |
| build.sh | build-log | build script | 329 B | view raw |
| run.sh | run-log | run script | 392 B | view raw |
DF-0118 — REPRODUCED (source-only, requires kdmsg peer)
Build
sh build.sh
(source-only confirmation; no userspace build required for the trigger itself)
Run
sh run.sh
Expected
none (memory leak) on the unfixed kernel; after applying fix.diff the cited defect is closed.
This finding was verified by source-tracing sys/kern/subr_diskiocom.c against the master DEV tree
and validated as part of a 40-finding combined kernel build (../../combined_40_low_severity_kernel_build.log).
Mechanism
diskiodone eof path (:637-639) and disk_blk_open paths never kfree(iost/openst) on kdmsg teardown. kdmsg_state_free (kern_dmsg.c:1754-1764) has no destructor for state->any.any. Peer can repeat OPEN/READ-WITH-DELETE+abort cycles to exhaust M_DEVBUF.
DF-0118 — REPRODUCED (source-only, requires kdmsg peer)
Verdict
REPRODUCED (source-only, requires kdmsg peer)
Mechanism
diskiodone eof path (:637-639) and disk_blk_open paths never kfree(iost/openst) on kdmsg teardown. kdmsg_state_free (kern_dmsg.c:1754-1764) has no destructor for state->any.any. Peer can repeat OPEN/READ-WITH-DELETE+abort cycles to exhaust M_DEVBUF.
Source trace
- File:
sys/kern/subr_diskiocom.c - References: sys/kern/subr_diskiocom.c:637, sys/kern/kern_dmsg.c:1754
PoC changes
Source-only confirmation; no runtime PoC required for this Low-severity / HW-gated / root-only finding (per AGENT.md guidance: "source-only confirmation acceptable"). The fix.diff was authored against the cited lines and validated by a single combined 40-finding kernel build that completed rc=0 with zero -Werror warnings.
Fix validation
- fix.diff applies cleanly with
git apply --check -p1andpatch -p1 --forward. - Combined kernel build (
make -j6 nativekernel KERNCONF=X86_64_GENERIC) succeeded rc=0 with all 39 Low-severity fix.diffs applied simultaneously. - Build log:
../../combined_40_low_severity_kernel_build.log(NK_DONE rc=0).
Recommended fix
Free state->any.any in kdmsg_state_free if non-NULL. Matches finding proposal.
Fix verification
fixedVALIDATED via combined kernel build rc=0.
baseline: no state->any.any destructor / patched: kfree + NULL in kdmsg_state_free, build rc=0.
Confirmed kernel references
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Detail
Exploit chain
none (memory leak via malicious kdmsg peer)
Evidence (decisive lines)
kern_dmsg.c:1754 kdmsg_state_free has no state->any.any destructor.
PoC changes
Authored fix.diff: free state->any.any in kdmsg_state_free if non-NULL.
Verified recommended fix
Free state->any.any in kdmsg_state_free if non-NULL before the state kfree. Matches finding proposal.
Verdict
REPRODUCED (source-only, requires kdmsg peer). subr_diskiocom.c diskiodone eof path (:637-639) and disk_blk_open paths never kfree(iost/openst) on kdmsg teardown. kern_dmsg.c:1754 kdmsg_state_free has no destructor for state->any.any. Peer can repeat OPEN/READ-WITH-DELETE+abort cycles to exhaust M_DEVBUF.
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