swap_pager_reserve leaks unused tail of last bulk allocation
Summary
swap_pager_reserve success path calls swp_pager_meta_free(object, start, n) at :785 where n is leftover swap blocks (1..63) from last swp_pager_getswapspace that were NEVER meta_build-ed. swp_pager_meta_free is a no-op for ranges with no metadata entries -> blocks never returned to blist -> permanently leaked from vm_swap_size/swapblist->bl_free. Only vn(4) driver calls it (VN_RESERVE, root-only). Repeated vn setup/teardown drains swap -> spurious swap-full. Fix: swp_pager_freeswapspace(object, blk-n, n) instead of meta_free.
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-0947 · 2 files| File | Type | Description | Size | |
|---|---|---|---|---|
| fix.diff | suggested-fix | git-apply-able fix for the cited path | 289 B | view raw |
| VERDICT.md | verdict | source-confirmation narrative | 979 B | ↓ raw |
DF-0947 source-confirmation
Verdict: REPRODUCED (source-confirmed)
Impact: dos Confidence: likely
Kernel ref: sys/vm/swap_pager.c:785
Mechanism
swap_pager_reserve meta_free's leftover blocks never returned to blist -> swap 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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- s
- w
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- p
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- p
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- g
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- .
- c
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- 7
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- 5
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: swap_pager_reserve meta_free's leftover blocks never returned to blist -> swap leak @ sys/vm/swap_pager.c:785. 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-0947/.
Verified recommended fix
freeswapspace the leftover tail blocks instead of meta_free (no-op). matches finding proposal. Full diff in findings/poc/DF-0947/fix.diff.
Verdict
REPRODUCED (source-confirmed). Source-trace confirmed swap_pager_reserve meta_free's leftover blocks never returned to blist -> swap leak at sys/vm/swap_pager.c:785 against the audited sys/ tree; exact line/condition verified.
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