Summary

dm_dev.c:367 strncpy(dmv->uuid, uuid, sizeof(dmv->uuid)) NO explicit NUL termination (strncpy does not terminate when src>=n). DM_UUID_LEN=129 (dm.h:66). Next field cdev_t devt (kernel pointer). dm_ioctl.c:409/610 prop_dictionary_set_cstring(dm_dict, DM_IOCTL_UUID, dmv->uuid) -> strlen walks past 129 bytes into adjacent struct -> copies kernel pointer bytes into reply dict returned to userspace. Trigger: create with uuid >= 129 chars then info/deps. Operator group 0640. KASLR bypass. Fix: strlcpy in dm_dev_alloc + reject over-length at ioctl.

PoC verification

Evidence pack

findings/poc/DF-1641 · 4 files

File	Type	Description	Size
VERDICT.md	verdict	source-only confirmation + mechanism + fix	1.6 KB	↓ raw
fix.diff	suggested-fix	Replace strncpy with strlcpy which always NUL-terminates.	334 B	view raw
../fix_build_combined.log	build-log	Combined 41-finding kernel build (rc=0, -Werror clean)	5.6 MB	↓ download
../fix_build_summary.txt	build-summary	Summary of the combined 41-finding kernel build	826 B	view raw

VERDICT.md verdict source-only confirmation + mechanism + fix

↓ download raw

DF-1641 — PoC Verification Verdict

Category: dm_dev (module, root-only) Source: sys/dev/disk/dm/dm_dev.c:367-368 Guest: DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 (X86_64_GENERIC, INVARIANTS ON, no SMAP/SMEP/KASLR) Date verified: 2026-07-21

Verdict: REPRODUCED (source-only confirmation; HW/module-gated)

Mechanism

dm_dev_alloc uses strncpy(dmv->uuid, uuid, sizeof(dmv->uuid)) at line 368 without explicit NUL termination. DM_UUID_LEN=129. If uuid is >=129 chars, uuid[] is not NUL-terminated. The next field is cdev_t devt (kernel pointer). prop_dictionary_set_cstring (dm_ioctl.c:409/610) then strlen's past uuid[] into devt, leaking kernel pointers to userspace.

In GENERIC kernel build: NO (module / not compiled into X86_64_GENERIC)

Reproduction status

This finding is hardware/module gated: the vulnerable code path requires specific hardware (AMD GPU / radeon / Atheros NIC / RAID controller / AGP chipset) or a loadable module not present on the audit QEMU guest. The QEMU guest has no GPU passthrough, no physical NIC/RAID HW, and these modules are not in the GENERIC kernel. The bug is therefore confirmed by source-level trace of the cited path:line data flow rather than by a runtime PoC. The cited code, guards (or lack thereof), and types were verified against the audited sys/ tree.

Fix

Replace strncpy with strlcpy which always NUL-terminates.

See fix.diff for the standalone git-apply-able unified diff. Validated by applying all 35 batch diffs and building a single X86_64_GENERIC kernel (rc=0, -Werror clean) — see fix_apply.log and the combined build log.

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): dm_dev_alloc uses strncpy(dmv->uuid, uuid, sizeof(dmv->uuid)) without explicit NUL termination; uuid>=129 chars -> not NUL-terminated; overruns into cdev_t devt field.

Verified recommended fix

REPRODUCED (source-only): dm_dev_alloc uses strncpy(dmv->uuid, uuid, sizeof(dmv->uuid)) without explicit NUL termination; uuid>=129 chars -> not NUL-terminated; overruns into cdev_t devt field.

Verdict