do_vmmeter_pcpu leaks kernel pointer v_lock_addr and token identifier to unprivileged users via vm.cpuN.vmmeter
Summary
do_vmmeter_pcpu at vm_meter.c:428-437 copies entire gd->gd_cnt struct and ships to user via sysctl_handle_opaque(sizeof(vmm)). struct vmmeter trailing fields v_lock_name[32] and void *v_lock_addr populated on every token/lock collision (lwkt_token.c:508,624; indefinite2.h:68,98). sysctl node CTLFLAG_RD only -> reads unrestricted for any local user/jail. sysctl vm.cpu0.vmmeter returns live kernel pointer (token/spinlock addr) + internal identifier string. Global do_vmmeter was hardened against this (bzero + loop bounded at vmmeter_uint_end=v_reserved7) but per-CPU variant missed. KASLR bypass + reveals specific synchronization object addresses. Fix: vmm.v_lock_addr=NULL + bzero v_lock_name before sysctl_handle_opaque.
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-0954 · 2 files| File | Type | Description | Size | |
|---|---|---|---|---|
| fix.diff | suggested-fix | git-apply-able fix for the cited path | 327 B | view raw |
| VERDICT.md | verdict | source-confirmation narrative | 982 B | ↓ raw |
DF-0954 source-confirmation
Verdict: REPRODUCED (source-confirmed)
Impact: leak Confidence: certain
Kernel ref: sys/vm/vm_meter.c:436
Mechanism
do_vmmeter_pcpu ships full vmmeter incl v_lock_addr/v_lock_name -> kernel pointer leak
Confirmation method
Source-trace confirmed the cited code path matches the finding (exact line/condition
verified against sys/). Runtime PoC not exercised for this source-only Low-severity
item; confirmation is by code inspection.
Recommended fix
See fix.diff in this folder (git-apply-able unified diff).
Phase 8 (combined build)
All 64 fixes were batched into one combined patch
(../_batch/combined_64.patch) and applied to in-guest /usr/src. A single
make -j6 nativekernel KERNCONF=X86_64_GENERIC completed rc=0 with 0 errors under
-Werror (../_batch/fix_build.log, 35374 lines). The GENERIC kernel + all modules
(drm, firewire, usb, netgraph, smbfs, fuse, crypto, vm, pmap) compiled clean.
Fix verification
not_testablenot_testable (source-only): no runtime PoC exercised; fix.diff applies cleanly and the combined single nativekernel build of all 64 fixes completed rc=0 with 0 errors under -Werror (findings/poc/_batch/fix_build.log). Bug source-confirmed in baseline tree. Compile-validation of the fix is the requested Phase-8 deliverable for this batch.
combined build: '=== NK_DONE rc=0 ===' and '>>> Kernel build for X86_64_GENERIC completed on Thu Jul 23 09:17:55 UTC 2026' (0 'error:' lines in 35374-line log).
Confirmed kernel references
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Detail
Exploit chain
none (non-corruption / source-only confirmation; no memory-corruption escalation chain developed for this Low-severity item)
Evidence (decisive lines)
source-only: do_vmmeter_pcpu ships full vmmeter incl v_lock_addr/v_lock_name -> kernel pointer leak @ sys/vm/vm_meter.c:436. Combined fix build: '=== NK_DONE rc=0 ===' / 'Kernel build for X86_64_GENERIC completed', 0 errors under -Werror (findings/poc/_batch/fix_build.log).
PoC changes
authored git-apply-able fix.diff targeting the cited line; source-trace verified the vulnerable path. Evidence pack (VERDICT.md, manifest.json, env.txt, fix.diff) in findings/poc/DF-0954/.
Verified recommended fix
zero v_lock_addr/v_lock_name before sysctl_handle_opaque. matches finding proposal. Full diff in findings/poc/DF-0954/fix.diff.
Verdict
REPRODUCED (source-confirmed). Source-trace confirmed do_vmmeter_pcpu ships full vmmeter incl v_lock_addr/v_lock_name -> kernel pointer leak at sys/vm/vm_meter.c:436 against the audited sys/ tree; exact line/condition verified.
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