DF-1101

Off-by-one write in decode_nfshandle corrupts root_saddr.sin_len, enabling OOB read via dup_sockaddr

Summary

decode_nfshandle at autoconf.c:366 writes *(fh++)=val at index len BEFORE checking if(len>NFSX_V2FH=32) at :369. With 33 hex byte pairs the 33rd byte overwrites root_fh[32] = root_saddr.sin_len (root_fh[NFSX_V2FH] immediately followed by root_saddr struct sockaddr_in in struct nfs_diskless per nfsdiskless.h:114). decode_nfshandle called at :479 AFTER inaddr_to_sockaddr populates root_saddr including sin_len=16 at :469. No code re-zeroes sin_len. When nfs_mountdiskless calls dup_sockaddr at nfs_vfsops.c:745, corrupted sin_len (up to 255) is used as kmalloc size AND bcopy length (uipc_socket2.c:813-814), reading 239 bytes past 16-byte root_saddr into root_hostnam/root_time/my_hostnam. VKERNEL64 config enables NFS+NFS_ROOT by default (:47-48); BOOTP_NFSROOT not defined so pxe_setup_nfsdiskless compiled. Trigger: -e boot.nfsroot.nfshandle=X<32 byte pairs><ff>X. Identical bug in pc64 autoconf.c:284-294 (more severe: leaks real kernel memory). Fix: move bounds check before write, change > to >=.

Discussion (0)

No comments yet.

Severity: Low
Status: new
Bucket: Kernel memory corruption (UAF / OOB write)
Confidence: certain
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
CWE: CWE-787 Out-of-bounds Write
File: sys/platform/vkernel64/x86_64/autoconf.c
Lines: 351-479
Area: hw
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 10:25:02
Attempts: —
Runtime: —
Code hash: —
Guest: DragonFly dfbsd 6.5-DEVELOPMENT #0
Build cmd: —
Run cmd: —

jump to evidence pack ↓

Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: certain
Tested: 2026-07-25 10:25:02
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1101/fix.diff
Runner: df-bsd-pocrunner

jump to fix verification ↓

PoC verification

Evidence pack

findings/poc/DF-1101 · 3 files

File	Type	Description	Size
VERDICT.md	verdict	Source-confirmation verdict for DF-1101	624 B	↓ raw
fix.diff	suggested-fix	Move bounds check before write in decode_nfshandle	396 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-1101

↓ download raw

DF-1101 Verification Verdict

Severity: Low Impact class: oob_write 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: Move bounds check before write in decode_nfshandle

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): decode_nfshandle writes *(fh++)=val at index len BEFORE checking len>NFSX_V2FH=32. With 33 hex byte pairs the 33rd byte overwrites root_fh[32] = root_saddr.sin_len. Stack OOB

Verified recommended fix

REPRODUCED (source-only): decode_nfshandle writes *(fh++)=val at index len BEFORE checking len>NFSX_V2FH=32. With 33 hex byte pairs the 33rd byte overwrites root_fh[32] = root_saddr.sin_len. Stack OOB write.