DF-0433

bpf_mtap_hdr submits partially-initialized stack mbuf: bpf_mtap reads uninitialized m_pkthdr.rcvif

Summary

bpf_mtap_hdr(:1347-1393): allocates only struct m_hdr on stack, initializes mh_flags/next/len/data but NOT m_pkthdr. Casts to struct mbuf* hands to bpf_mtap(). bpf_mtap(:1322) reads m->m_pkthdr.rcvif in control-flow check (!bd_seesent&&rcvif==NULL). m_pkthdr past end of stack m_hdr -> reads adjacent uninitialized stack bytes. Contrast bpf_ptap(:1377-1393) correctly inits rcvif. Rare driver caller + bd_seesent cleared. No confirmed leak to userspace (bpf_mcopy uses initialized m_len/m_data/m_next).

Discussion (0)

No comments yet.

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:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
CWE: CWE-908
File: sys/net/bpf.c
Lines: 1347-1393
Area: net
Discovered: 2026-07-01
Updated: 2026-07-01

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: dos
Confidence: likely
Tested: 2026-07-23 04:51:47
Attempts: 1
Runtime: —
Code hash: 22b1e8c38c7d962e
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)

jump to evidence pack ↓

Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: likely
Tested: 2026-07-23 04:51:47
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-0433/fix.diff
Runner: df-bsd-pocrunner

jump to fix verification ↓

PoC verification

Evidence pack

findings/poc/DF-0433 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	source verification verdict	699 B	↓ raw
fix.diff	suggested-fix	fix for uninit bug	539 B	view raw

VERDICT.md verdict source verification verdict

↓ download raw

DF-0433 - Verification Verdict

Verdict: REPRODUCED (source-only confirmation)

Bug class: uninit

Impact: dos

Source file: sys/net/bpf.c

Mechanism

CONFIRMED: bpf_mtap_hdr allocates only struct m_hdr on stack, doesn't init m_pkthdr. bpf_mtap reads m->m_pkthdr.rcvif. Fix: use full struct mbuf.

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/net/bpf.c:1347.

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/net/bpf.c:1347. Combined kernel build with all 70 fixes: rc=0, -Werror.

PoC changes

Created fix.diff for DF-0433. No PoC binary (source-only verification).

Verified recommended fix

Use full struct mbuf instead of m_hdr. Supersedes finding proposal.

Verdict

CONFIRMED source-only: bpf_mtap_hdr only allocates m_hdr, no m_pkthdr init. bpf_mtap reads rcvif.