Uninitialized kernel stack memory disclosed via vm.resident sysctl
Summary
sysctl_vm_resident: struct xresident xres on stack uninitialized(:148). fill_xresident: struct st uninitialized(:82). On vget/vn_stat failure paths(:103-105,:108-111 goto done), res_stat never written. SYSCTL_OUT(:153) copies entire struct including uninitialized stack -> kernel addr/pointer leak. Root-only (SYSCAP_NOVM_RESIDENT gate).
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-0182 · 5 files| File | Type | Description | Size | |
|---|---|---|---|---|
| VERDICT.md | verdict | source-trace confirmation + fix rationale | 1.6 KB | ↓ raw |
| fix.diff | suggested-fix | git-apply-able fix for DF-0182 | 339 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 |
DF-0182 — Uninitialized kernel stack memory disclosed via vm.resident sysctl
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. sysctl_vm_resident: struct xresident xres on stack(:148) uninitialized; fill_xresident: struct stat st(:82) uninitialized. On vget/vn_stat failure paths(:103-105,:108-111 goto done), res_stat never written. SYSCTL_OUT(:153) copies the entire struct including uninitialized stack → kernel pointer leak. Root-only (SYSCAP_NOVM_RESIDENT gate).
Kernel references (confirmed)
Fix
bzero xres before fill_xresident. 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-0182/../../_combined_build.log(reference; full log at audit time). - Combined kernel.stripped sha256:
9337c4e114e3a91edc02fee6d9eff48799b3c0926c1151d642b4573cb7911000 - Build completed: 2026-07-22T22:33:21Z
Fix verification
fixedVALIDATED via combined build (rc=0).
NK_DONE rc=0; errors:0
Confirmed kernel references
- s
- y
- s
- /
- k
- e
- r
- n
- /
- i
- m
- g
- a
- c
- t
- _
- r
- e
- s
- i
- d
- e
- n
- t
- .
- c
- :
- 8
- 2
- s
- y
- s
- /
- k
- e
- r
- n
- /
- i
- m
- g
- a
- c
- t
- _
- r
- e
- s
- i
- d
- e
- n
- t
- .
- c
- :
- 1
- 4
- 8
- s
- y
- s
- /
- k
- e
- r
- n
- /
- i
- m
- g
- a
- c
- t
- _
- r
- e
- s
- i
- d
- e
- n
- t
- .
- c
- :
- 1
- 5
- 3
Detail
Exploit chain
none — Low-severity source-only confirmation.
Evidence (decisive lines)
Source-trace confirmed at sys/kern/imgact_resident.c:82, sys/kern/imgact_resident.c:148, sys/kern/imgact_resident.c:153. Combined build rc=0.
PoC changes
Authored fix.diff in findings/poc/DF-0182/.
Verified recommended fix
bzero xres before fill_xresident; supersedes finding proposal.
Verdict
CONFIRMED. sysctl_vm_resident: xresident xres(:148) and stat st(:82) on stack uninitialized; failure paths skip writes; SYSCTL_OUT(:153) copies entire struct -> stack leak. Root-only.
No comments yet.