DF-0491

NULL td dereference in SIOCSIFDSTADDR and default ioctl handlers despite documented td might be NULL contract

Summary

in_control(:221) documents td might be NULL. Priv guards(:513,:561) use if(td&&...) skip when NULL. But SIOCSIFDSTADDR handler(:606) ifp->if_ioctl(ifp,SIOCSIFDSTADDR,(caddr_t)ia,td->td_proc->p_ucred) derefs td unconditionally. Default-case handler(:735) same pattern. Kernel-initiated path with td=NULL for these cmds -> NULL-page fault panic. Not reachable from unpriv userspace (td always non-NULL for user ioctls). Latent crash bug contradicts API contract. Fix: if(td==NULL) return EINVAL or use proc0.p_ucred fallback.

Discussion (0)

No comments yet.

Severity: Low
Status: new
Bucket: Base system — network stack
Confidence: likely
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U:C:N/I:N/A:H
CWE: CWE-476
File: sys/netinet/in.c
Lines: 606-735
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 04:51:50
Attempts: 1
Runtime: —
Code hash: f8a3e1dbdb44efa3
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 04:51:50
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-0491/fix.diff
Runner: df-bsd-pocrunner

jump to fix verification ↓

PoC verification

Evidence pack

findings/poc/DF-0491 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	source verification verdict	710 B	↓ raw
fix.diff	suggested-fix	fix for null-deref bug	409 B	view raw

VERDICT.md verdict source verification verdict

↓ download raw

DF-0491 - Verification Verdict

Verdict: REPRODUCED (source-only confirmation)

Bug class: null-deref

Impact: dos

Source file: sys/netinet/in.c

Mechanism

CONFIRMED: in_control documents td might be NULL but SIOCSIFDSTADDR and default-case deref td->td_proc->p_ucred unconditionally. Fix: check td!=NULL.

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/in.c:609.

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/in.c:609. Combined kernel build with all 70 fixes: rc=0, -Werror.

PoC changes

Created fix.diff for DF-0491. No PoC binary (source-only verification).

Verified recommended fix

Check td!=NULL before p_ucred deref. Matches finding proposal.

Verdict

CONFIRMED source-only: in_control SIOCSIFDSTADDR derefs td->td_proc->p_ucred when td may be NULL.