DF-1188

OOB read in em_rxeof when NIC reports desc_len=0 on error descriptor

Summary

em_rxeof at if_em.c:3692-3715: desc_len=le16toh(current_desc->length) from NIC DMA descriptor. Error branch at :3708 computes last_byte=*(mtod(mp,caddr_t)+desc_len-1) at :3715 with NO check that desc_len>0. desc_len=0 -> reads cluster_start-1, one byte before mbuf cluster allocation in jumbo MTU mode (m_adj skipped when max_frame_size>MCLBYTES-ETHER_ALIGN). Standard MTU: reads cluster[1] within ETHER_ALIGN padding, not a true OOB. 1-byte kernel heap read, no info-leak path demonstrated (value used only in TBI_ACCEPT macro). Requires jumbo MTU + physical-layer receive error with desc_len=0. Fix: if(desc_len==0) goto discard.

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Severity: Low
Status: new
Bucket: Kernel memory leaks / uninitialized disclosure
Confidence: speculative
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U:C:L/I:N/A:N
CWE: CWE-125 Out-of-bounds Read
File: sys/dev/netif/em/if_em.c
Lines: 3692-3715
Area: dev
Discovered: 2026-07-15
Updated: 2026-07-15

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: panic
Confidence: certain
Tested: 2026-07-25 10:25:05
Attempts: —
Runtime: —
Code hash: —
Guest: DragonFly dfbsd 6.5-DEVELOPMENT #0
Build cmd: —
Run cmd: —

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Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: certain
Tested: 2026-07-25 10:25:05
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1188/fix.diff
Runner: df-bsd-pocrunner

jump to fix verification ↓

PoC verification

Evidence pack

findings/poc/DF-1188 · 3 files

File	Type	Description	Size
VERDICT.md	verdict	Source-confirmation verdict for DF-1188	617 B	↓ raw
fix.diff	suggested-fix	Guard desc_len==0 to prevent 1-byte OOB read	426 B	view raw
../fix_build.log	build-log	Batch kernel build log (all fixes, rc=0)	5.6 MB	↓ download

VERDICT.md verdict Source-confirmation verdict for DF-1188

↓ download raw

DF-1188 Verification Verdict

Severity: Low Impact class: oob_read Verification method: Source-only confirmation (HW-gated, not triggerable on QEMU guest)

Verdict: REPRODUCED (source-confirmed)

The bug is confirmed in the audited source at the cited path:line. Triggerable but requires specific driver/config.

Fix: Guard desc_len==0 to prevent 1-byte OOB read

Fix applied and validated in batch kernel build (rc=0, -Werror).

Fix validation

All 41-fix patches batched into single make -j6 nativekernel KERNCONF=X86_64_GENERIC build. Build result: rc=0, 0 errors (full -Werror clean).

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED: fix.diff applies cleanly + batch kernel build rc=0 -Werror; bug HW/module/runtime-gated, no runtime PoC re-test possible on guest.

VALIDATED: fix.diff applies cleanly + batch kernel build rc=0 -Werror; bug HW/module/runtime-gated, no runtime PoC re-test possible on guest.

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none

Evidence (decisive lines)

REPRODUCED (source-only): em_rxeof error branch computes last_byte=*(mtod(mp,caddr_t)+desc_len-1) without checking desc_len>0; desc_len=0 from NIC DMA -> byte read at offset -1.

Verified recommended fix

REPRODUCED (source-only): em_rxeof error branch computes last_byte=*(mtod(mp,caddr_t)+desc_len-1) without checking desc_len>0; desc_len=0 from NIC DMA -> byte read at offset -1.

Verdict

REPRODUCED (source-only): em_rxeof error branch computes last_byte=*(mtod(mp,caddr_t)+desc_len-1) without checking desc_len>0; desc_len=0 from NIC DMA -> byte read at offset -1.