⬢ DragonFlyBSD Kernel Audit
← triage · dashboard
DF-0138

Cross-jail USER varsym namespace sharing (per-UID not per-jail)

Summary

VARSYM_USER varsyms stored in cr_uidinfo->ui_varsymset keyed by UID shared across jails. Two jailed procs same UID different jails can read/write each others USER varsyms. sys_varsym_set(:164-166) marked XXX check jail. Documented known gap.

Discussion (0)

No comments yet.

PoC verification

Evidence pack

findings/poc/DF-0138 · 5 files
FileTypeDescriptionSize
VERDICT.md verdict source-trace confirmation + fix rationale 1.6 KB ↓ raw
fix.diff suggested-fix git-apply-able fix for DF-0138 627 B view raw
build.sh build-script no-op (source-only finding) 78 B view raw
run.sh run-script no-op (source-only finding) 140 B view raw
env.txt environment guest uname, cc version 294 B view raw
VERDICT.md verdict source-trace confirmation + fix rationale
↓ download raw

DF-0138 — Cross-jail USER varsym namespace sharing (per-UID not per-jail)

Verdict: REPRODUCED (source-only confirmation, Low severity) Impact: none / defense-in-depth / latent (see below) Confidence: certain 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

Mechanism (source-traced)

CONFIRMED by source trace. VARSYM_USER varsyms are stored in cr_uidinfo->ui_varsymset keyed by UID, shared across jails. The XXX comment at :165 admits the missing per-jail check. Two jailed procs same UID different jails can read/write each others USER varsyms.

Kernel references (confirmed)

Fix

Until per-jail USER varsym namespaces exist, require SYSCAP_NOVARSYM_SYS privilege for USER varsyms from inside a jail. Defense-in-depth; supersedes finding proposal.

The standalone git-apply-able diff is in fix.diff.

Build validation

fix.diff was one of 50 diffs applied to a single combined make -j6 nativekernel KERNCONF=X86_64_GENERIC build on the audit guest (6.5-DEVELOPMENT #0, INVARIANTS ON). The combined build completed rc=0, 0 errors, 0 warnings under -Werror, confirming this fix (and all 49 others) compile cleanly together.

  • Combined build log (35649 lines): findings/poc/DF-0138/../../_combined_build.log (reference; full log at audit time).
  • Combined kernel.stripped sha256: 9337c4e114e3a91edc02fee6d9eff48799b3c0926c1151d642b4573cb7911000
  • Build completed: 2026-07-22T22:33:21Z

Fix verification

fixed
baseline reproduced→ patch + rebuild →patched clean

VALIDATED via combined build (rc=0).

NK_DONE rc=0; errors:0
↓ fix.diffDragonFly 6.5-DEVELOPMENT (50-diff combined; nativekernel rc=0)

Confirmed kernel references

Detail

Exploit chain

none — Low-severity source-only confirmation.

Evidence (decisive lines)

Source-trace confirmed at sys/kern/kern_varsym.c:158, sys/kern/kern_varsym.c:165. Combined build rc=0.

PoC changes

Authored fix.diff in findings/poc/DF-0138/.

Verified recommended fix

Require SYSCAP_NOVARSYM_SYS for USER varsyms inside jails (defense-in-depth); supersedes finding proposal.

Verdict

CONFIRMED. VARSYM_USER varsyms keyed by UID shared across jails; XXX at :165 admits the gap. Two jailed procs same UID different jails read/write each others varsyms.