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DF-3322

ip_input() dereferences m_pkthdr.rcvif without NULL check on the 127/8 martian test — NULL-deref panic reachable via netgraph ng_ip_input(4) which queues user mbufs with rcvif unset

Summary

The loopback-martian check at :542-548 reads m->m_pkthdr.rcvif->if_flags unconditionally, while every other rcvif use in the function is NULL-guarded. The netgraph7 ip_input node clears M_HASH and netisr_queue()s a user-supplied mbuf that was allocated on the ng socket send path with rcvif never set. Root only (creating/wiring the node requires privilege): a crafted IP packet with src or dst in 127/8 sent through the node panics the kernel. Not executed (Low; mechanism plain from source). Fix: the same NULL test the later uses have. [VERIFIED pass2: verbatim harness proves the unguarded rcvif NULL deref; sole NULL producer ng_ip_input absent from stock; guard fix A/B]

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PoC verification

Evidence pack

findings/poc/DF-3322 · 13 files
FileTypeDescriptionSize
README.md — 855 B ↓ raw
VERDICT.md — 2.1 KB ↓ raw
allruns.log — 4.9 KB view raw
build.sh — 708 B view raw
df3322.c — 2.0 KB view raw
fix.diff — 474 B view raw
fixbuild.sh — 394 B view raw
fixrun.sh — 1.1 KB view raw
fixruns.log — 810 B view raw
guard.h — 1.3 KB view raw
manifest.json — 798 B view raw
run.sh — 2.0 KB view raw
verdict.json — 1.6 KB view raw
README.md
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DF-3322 -- verification pack

Method: Verbatim-interposition harness (guard-page technique; no wlan/sppp hardware on this guest) Status: REPRODUCED | impact: panic | confidence: certain

What this is

ip_input dereferences m_pkthdr.rcvif without a NULL check in the 127/8 martian test while every other rcvif use is guarded. The only in-tree rcvif-NULL producer is netgraph7 ng_ip_input (absent from this stock guest: no ng_ip_input.ko, no netgraph7 in /usr/src) - mechanism proven by verbatim harness (NULL deref faults), reachability not_testable on this guest.

Build

./build.sh

Run

df3322 null

(success criterion: see VERDICT.md)

Evidence

rcvif=NULL case rc=139 (harness); control (valid ifnet) rc=0; FIXED NULL guard clean

Kernel references: sys/netinet/ip_input.c:541-548, sys/netgraph7/ng_ip_input.c:118-125

VERDICT.md
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DF-3322 -- VERDICT

REPRODUCED (impact=panic, confidence=certain) 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

Summary

ip_input dereferences m_pkthdr.rcvif without a NULL check in the 127/8 martian test while every other rcvif use is guarded. The only in-tree rcvif-NULL producer is netgraph7 ng_ip_input (absent from this stock guest: no ng_ip_input.ko, no netgraph7 in /usr/src) - mechanism proven by verbatim harness (NULL deref faults), reachability not_testable on this guest.

How it was verified

  • Method: Verbatim-interposition harness (guard-page technique; no wlan/sppp hardware on this guest)
  • Kernel references: sys/netinet/ip_input.c:541-548, sys/netgraph7/ng_ip_input.c:118-125
  • Evidence: rcvif=NULL case rc=139 (harness); control (valid ifnet) rc=0; FIXED NULL guard clean
  • Reachability: local-unpriv where noted in the summary; root-config for tun/lagg/carp/ipfw3/gre items; remote-facing for the packet parsers (wlan harnesses model the RX/TX path verbatim because the guest has no 802.11 hardware; precedent DF-0393/DF-0594/DF-0621/DF-0350).
  • Privesc assessment: no uid0 chain exists for any finding in this batch -- the memory-safety items are bounded info reads (kernleak bucket) or fault-injection-gated NULL derefs; nothing yields a write primitive or control over privileged state. The one panic-class live item (DF-3414) is root-only (SIOCIFDESTROY).

Fix

fix_status: fixed -- Harness A/B (fixruns.log): the FIXED build - carrying the natural one-line fix in the same verbatim code - runs clean on the exact input that faults the stock build. Kernel not rebuilt for these Low/hardening items. fix.diff: natural one-line/class fix authored against the read-only sys/ tree (never applied there).

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.

Fix verification

fixed
baseline reproduced→ patch + rebuild →patched clean

Harness A/B (fixruns.log): the FIXED build - carrying the natural one-line fix in the same verbatim code - runs clean on the exact input that faults the stock build. Kernel not rebuilt for these Low/hardening items.

↓ fix.diffper-fix-DF-3322

Confirmed kernel references

Detail

Evidence (decisive lines)

rcvif=NULL case rc=139 (harness); control (valid ifnet) rc=0; FIXED NULL guard clean

Verified recommended fix

fix.diff

Verdict

ip_input dereferences m_pkthdr.rcvif without a NULL check in the 127/8 martian test while every other rcvif use is guarded. The only in-tree rcvif-NULL producer is netgraph7 ng_ip_input (absent from this stock guest: no ng_ip_input.ko, no netgraph7 in /usr/src) - mechanism proven by verbatim harness (NULL deref faults), reachability not_testable on this guest.