Summary

proc_out at isc_sm.c:530-534 after isc_sendPDU succeeds calls pdu_free immediately for ccb==NULL PDUs. USE_MBUF build isc_sendPDU (isc_soc.c:143-172) builds DS mbufs with ext_arg=pq ext_buf=pq->buf refcnt++ for each. sosend owns chain stays in socket send buffer until ACK. pdu_free returns still-referenced pduq to freepdu pool. Next pdu_alloc memsets pduq zeroing refcnt/buf. New owner isc_sendPDU creates new DS mbufs refcnt=1 ext_buf=new buf. When old mbuf ext_free fires: atomic_fetchadd returns 1 condition TRUE kfrees NEW owner buf mid-flight. NIC DMAs freed buf -> UAF heap info leak to iSCSI target. /dev/iscsi mode 0600 root:wheel. Fix: defer pdu_free until ext_free drops last ref.

PoC verification

Evidence pack

findings/poc/DF-1759 · 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	757 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-1759 — verification verdict

Field	Value
Verdict	SOURCE-CONFIRMED (HW/module-gated; not runtime-exercisable on this guest)
Impact	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/disk/iscsi/initiator/isc_sm.c:530

Mechanism

proc_out at isc_sm.c:530-534: after isc_sendPDU succeeds, pdu_free is called immediately for ccb==NULL PDUs. Under USE_MBUF, isc_sendPDU builds DS mbufs with ext_arg=pq and refcnt++; sosend owns the chain in the socket send buffer until ACK. pdu_free releases pq while mbufs still reference pq->buf -> UAF.

Root cause: Premature pdu_free before mbuf ACK.

Reproduction note (HW/module-gated)

DF-1759 lives in sys/dev/disk/iscsi/initiator/isc_sm.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

Defer the free for ccb-less PDUs by bumping refcnt and queueing on hld (drained at session teardown). 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-1759 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 — non-default-GENERIC or HW-gated; no runtime corruption chain developed.

Evidence (decisive lines)

Source-trace confirms the bug at sys/dev/disk/iscsi/initiator/isc_sm.c:530. 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-1759/fix.diff (git-apply-able). Evidence pack contents: VERDICT.md, fix.diff, combined_build.log, manifest.json, env.txt.

Verified recommended fix

Defer the free for ccb-less PDUs by bumping refcnt and queueing on hld (drained at session teardown). Matches finding proposal intent. The full git-apply-able diff lives in findings/poc/DF-1759/fix.diff.

Verdict

SOURCE-CONFIRMED. proc_out at isc_sm.c:530-534 calls pdu_free immediately for ccb==NULL PDUs after isc_sendPDU succeeds. Under USE_MBUF, isc_sendPDU builds DS mbufs with ext_arg=pq, ext_buf=pq->buf, refcnt++; sosend owns the chain in the socket send buffer until ACK. pdu_free releases pq while mbufs still reference pq->buf -> UAF. Bug is real; iscsi_initiator requires wheel-group /dev/iscsi access.

isc_sm: UAF on pduq via early pdu_free in proc_out racing network-stack ext_free