⬢ DragonFlyBSD Kernel Audit
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DF-3442

iface_match(): kfnmatch() on a rule-supplied, not-guaranteed-NUL-terminated via/xmit/recv interface name reads past the instruction/rule allocation

Summary

check_via() calls iface_match(), which when cmd->p.glob is set runs kfnmatch(cmd->name, ifp->if_xname, 0) on the 16-byte name[] embedded in ipfw_insn_if. Rule bodies are copied verbatim from the control socket (no instruction validation, cf. DF-0472), so a rule with all 16 name bytes non-NUL makes kfnmatch's pattern walk continue past name[16]; if the via instruction is the last in the rule, the read crosses the end of the rule's kmalloc'd chunk into adjacent zone memory. Non-glob matches use bounded strncmp (safe). Root-crafted rule, packet-triggered read; impact is a 1-bit match oracle / rare crash, no demonstrated disclosure. The ipfw2 twin is DF-3262 (variant family). Fix: require memchr(cmd->name, 0, IFNAMSIZ) before kfnmatch. [VERIFIED pass2: reproduced via guard harness - non-NUL-terminated rule name walks past the rule allocation, needs hand-crafted root setsockopt; termination-check fix A/B]

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PoC verification

Evidence pack

findings/poc/DF-3442 · 13 files
FileTypeDescriptionSize
README.md — 833 B ↓ raw
VERDICT.md — 2.1 KB ↓ raw
allruns.log — 4.9 KB view raw
build.sh — 708 B view raw
df3442.c — 2.1 KB view raw
fix.diff — 319 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 — 806 B view raw
run.sh — 2.0 KB view raw
verdict.json — 1.6 KB view raw
README.md
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DF-3442 -- verification pack

Method: Verbatim-interposition harness (guard-page technique; no wlan/sppp hardware on this guest) Status: REPRODUCED | impact: none | confidence: certain

What this is

iface_match() runs kfnmatch() on rule-supplied via/xmit/recv names the kernel never validates for NUL termination. Stock ipfw3(8) terminates via strlcpy (libipfw3 fill_iface), so exposure needs a hand-crafted root setsockopt; harness (fnmatch == kfnmatch semantics) with a 16-byte all-glob non-terminated name faults the guard page.

Build

./build.sh

Run

df3442 oob

(success criterion: see VERDICT.md)

Evidence

non-terminated glob name rc=139; terminated control rc=0; FIXED termination check clean

Kernel references: sys/net/ipfw3_basic/ip_fw3_basic.c:134-141, sys/net/ipfw3/ip_fw3.h:191-198

VERDICT.md
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DF-3442 -- VERDICT

REPRODUCED (impact=none, 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

iface_match() runs kfnmatch() on rule-supplied via/xmit/recv names the kernel never validates for NUL termination. Stock ipfw3(8) terminates via strlcpy (libipfw3 fill_iface), so exposure needs a hand-crafted root setsockopt; harness (fnmatch == kfnmatch semantics) with a 16-byte all-glob non-terminated name faults the guard page.

How it was verified

  • Method: Verbatim-interposition harness (guard-page technique; no wlan/sppp hardware on this guest)
  • Kernel references: sys/net/ipfw3_basic/ip_fw3_basic.c:134-141, sys/net/ipfw3/ip_fw3.h:191-198
  • Evidence: non-terminated glob name rc=139; terminated control rc=0; FIXED termination check 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-3442

Confirmed kernel references

Detail

Evidence (decisive lines)

non-terminated glob name rc=139; terminated control rc=0; FIXED termination check clean

Verified recommended fix

fix.diff

Verdict

iface_match() runs kfnmatch() on rule-supplied via/xmit/recv names the kernel never validates for NUL termination. Stock ipfw3(8) terminates via strlcpy (libipfw3 fill_iface), so exposure needs a hand-crafted root setsockopt; harness (fnmatch == kfnmatch semantics) with a 16-byte all-glob non-terminated name faults the guard page.