DF-0360

nm_dump_buf writes unbounded hex dump into fixed 8 KiB static buffer _dst

Summary

nm_dump_buf(:322-361): when dst=NULL uses static char _dst[8192](:325). Header comment states "buffer must be at least 30+4*len" but static fallback is fixed 8KB. Per-line hexdump loop(:341-355) emits ~71 bytes/iter with no capacity check. Caller passing len>~2040 with dst=NULL overruns .bss. Latent: gated by netmap_verbose debug path. Hardening.

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Severity: Low
Status: new
Bucket: Kernel memory corruption (UAF / OOB write)
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:N/I:N/A:L
CWE: CWE-120
File: sys/net/netmap/netmap.c
Lines: 322-361
Area: net
Discovered: 2026-07-01
Updated: 2026-07-01

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: none
Confidence: likely
Tested: 2026-07-23 04:51:42
Attempts: 1
Runtime: —
Code hash: 21dc8d4b922d07ea
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 04:51:42
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-0360/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-0360 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	source verification verdict	693 B	↓ raw
fix.diff	suggested-fix	fix for overflow bug	342 B	view raw

VERDICT.md verdict source verification verdict

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DF-0360 - Verification Verdict

Verdict: REPRODUCED (source-only confirmation)

Bug class: overflow

Impact: none

Source file: sys/net/netmap/netmap.c

Mechanism

CONFIRMED: nm_dump_buf uses static 8KB buffer but header says 30+4*len needed. Large len overruns .bss. Latent debug function.

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/netmap/netmap.c:325.

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/netmap/netmap.c:325. Combined kernel build with all 70 fixes: rc=0, -Werror.

PoC changes

Created fix.diff for DF-0360. No PoC binary (source-only verification).

Verified recommended fix

Add NM_DUMP_MAXLEN define for capacity awareness. Supersedes finding proposal.

Verdict

CONFIRMED source-only: static _dst[8192] can overflow with large len. Debug function.