DF-0344

No re-validation of m_len>=hlen after pfil hook rewrite/dummynet re-entry

Summary

After pfil_run_hooks(:631) rewrites packet, hlen re-derived from ip->ip_vhl(:635) with no m_len check or pullup. ip_dooptions(:661) walks hlen-20 option bytes. Buggy pfil hook with inconsistent ip_vhl/m_len -> OOB read in option loop. Requires pfil module defect, not reachable via crafted packets alone.

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Severity: Low
Status: new
Bucket: Kernel memory leaks / uninitialized disclosure
Confidence: likely
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
CWE: CWE-20
File: sys/netinet/ip_input.c
Lines: 631-661
Area: net
Discovered: 2026-06-30
Updated: 2026-06-30

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: dos
Confidence: likely
Tested: 2026-07-23 04:51:41
Attempts: 1
Runtime: —
Code hash: 08ffae36da1da6f1
Guest: DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 x86_64
Build cmd: n/a (source-only verification)
Run cmd: n/a (source-only verification)

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Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: likely
Tested: 2026-07-23 04:51:41
Runtime: —
Kernel: 6.5-DEVELOPMENT #0 (combined-fix build, rc=0 -Werror, Thu Jul 23 04:36:20 UTC 2026)
fix.diff: findings/poc/DF-0344/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-0344 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	source verification verdict	797 B	↓ raw
fix.diff	suggested-fix	fix for logic bug	454 B	view raw

VERDICT.md verdict source verification verdict

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DF-0344 - Verification Verdict

Verdict: REPRODUCED (source-only confirmation)

Bug class: logic

Impact: dos

Source file: sys/netinet/ip_input.c

Mechanism

CONFIRMED: After pfil_run_hooks, hlen re-derived from ip->ip_vhl without m_len check or pullup. Buggy pfil hook with inconsistent ip_vhl/m_len could cause OOB read in ip_dooptions option loop. Defense-in-depth: add m_pullup after pfil.

Fix

See fix.diff for the git-apply-able patch.

Build validation

Combined kernel build with all 70 Low-severity fixes: rc=0, -Werror. All fixes compile cleanly in X86_64_GENERIC kernel configuration.

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

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED: fix.diff compiles cleanly in combined kernel build (rc=0, -Werror). Source trace confirms bug at sys/netinet/ip_input.c:635.

Combined build: 70 fix.diffs applied to /usr/src, nativekernel KERNCONF=X86_64_GENERIC rc=0 -Werror. All fixes compile.

↓ fix.diff6.5-DEVELOPMENT #0 (combined-fix build, rc=0 -Werror, Thu Jul 23 04:36:20 UTC 2026)

Confirmed kernel references

Detail

Exploit chain

none (non-corruption Low severity finding; source-only confirmation)

Evidence (decisive lines)

Source-traced at sys/netinet/ip_input.c:635. Combined kernel build with all 70 fixes: rc=0, -Werror.

PoC changes

Created fix.diff for DF-0344. No PoC binary (source-only verification).

Verified recommended fix

Add m_pullup after pfil_run_hooks to validate packet header. Supersedes finding proposal.

Verdict

CONFIRMED source-only: After pfil hooks, hlen re-derived from ip_vhl without m_len check/pullup. Defense-in-depth.