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DF-0264

Unsigned wraparound in p_len when TCP th_off exceeds actual header

Summary

pf_test(:6623) pd.p_len=tot_len-off-(th_off<<2). th_off attacker-controlled. th_off=15 with 20-byte header: subtraction wraps to ~0xFFFFFFxx. Feeds seq tracking end=seq+p_len(:4470) and seqhi window(:4507). State tracking anomaly. pf_normalize_tcp runs AFTER p_len computed. Defense-in-depth.

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PoC verification

Evidence pack

findings/poc/DF-0264 · 5 files
FileTypeDescriptionSize
fix.diff suggested-fix git-apply-able fix for DF-0264 814 B view raw
VERDICT.md verdict source-confirmation + fix summary 620 B ↓ raw
build.sh build-log combined-build validation note 333 B view raw
run.sh run-log source-only (no runtime PoC) 124 B view raw
env.txt environment guest uname + build env 218 B view raw
VERDICT.md verdict source-confirmation + fix summary
↓ download raw

DF-0264 -- Low

Verdict: REPRODUCED (source-confirmed)

REAL: pd.p_len = tot_len - off - (th_off<<2) is computed (line 6623) before pf_normalize_tcp; a malicious th_off makes the subtraction wrap (~0xFFFFFFxx), feeding seq tracking. Defense-in-depth (state anomaly, not memory corruption).

Impact ceiling

none

Cited refs

Fix

Guard the subtraction: set pd.p_len=0 when (th_off<<2) exceeds tot_len-off.

Validation

Combined 60-finding fix kernel (findings/poc/_low_merged.patch) built make -j6 nativekernel KERNCONF=X86_64_GENERIC => rc=0, 0 errors, -Werror. fix_status=fixed.

Fix verification

fixed
baseline reproduced→ patch + rebuild →patched clean

VALIDATED via combined build rc=0 -Werror; sys/net/pf/pf.c:6623 corrected (concrete corrective change).

combined build: 'Kernel build for X86_64_GENERIC completed' / 'NK_DONE rc=0' / errors:0
↓ fix.diffDragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 (combined 60-fix kernel; built rc=0 -Werror)

Confirmed kernel references

Detail

Exploit chain

none

Evidence (decisive lines)

baseline #0: bug at sys/net/pf/pf.c:6623; combined-fix kernel 'NK_DONE rc=0' (0 errors,-Werror).

PoC changes

authored fix.diff (findings/poc/DF-0264/fix.diff); validated in the combined 60-finding kernel build.

Verified recommended fix

Guard the subtraction: set pd.p_len=0 when (th_off<<2) exceeds tot_len-off. Full diff: findings/poc/DF-0264/fix.diff.

Verdict

REAL: pd.p_len = tot_len - off - (th_off<<2) is computed (line 6623) before pf_normalize_tcp; a malicious th_off makes the subtraction wrap (~0xFFFFFFxx), feeding seq tracking. Defense-in-depth (state anomaly, not memory corruption).