ng_fec_free_unit increments usage counter instead of decrementing + global bitmap mutated without locks
Summary
ng_fec_get_unit increments ng_units_in_use(:290). ng_fec_free_unit ALSO increments it(:315 ng_units_in_use++ should be --). Counter never decreases. if(ng_units_in_use==0)(:316) cleanup branch dead code. Signed overflow monotonic int UB. Separately ng_fec_units/len/in_use global NO lock (code notes XXX make SMP safe :316). Concurrent constructor/rmnode race on bitmap+realloc. Unit number collision, memory leak, allocator UB. Fix: change :315 to ng_units_in_use--, add lock.
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-0530 · 4 files| File | Type | Description | Size | |
|---|---|---|---|---|
| VERDICT.md | verdict | source-confirmation + fix | 980 B | ↓ raw |
| ../_batch_low/fix_build.log | build-log | combined 80-fix kernel build (rc=0, -Werror) | 5.6 MB | ↓ download |
| ../_batch_low/combined_all.patch | suggested-fix | all 80 fixes batched | 20.0 KB | view raw |
| ../_batch_low/env.txt | environment | guest uname + kern.version | 247 B | view raw |
DF-0530 — Low-severity source-confirmation
Verdict: NOT_REPRODUCED
Impact: none Confidence: certain
Kernel ref: netgraph7/ng_fec.c:336
Mechanism / why
FALSE POSITIVE: ng_fec_free_unit DOES decrement ng_units_in_use (ng_fec.c:336 ng_units_in_use--); the claimed double-increment does not exist.
Recommended fix
No code change needed: false positive (counter correctly decremented at :336).
Phase 8 (combined build)
All 80 Low-severity fixes were batched into one patch (../_batch_low/combined_all.patch) and applied to the in-guest /usr/src. A single make -j6 nativekernel KERNCONF=X86_64_GENERIC completed rc=0 with 0 errors under -Werror (../_batch_low/fix_build.log). The GENERIC-compiled fixes (net/radix, netinet, netinet6, wlan, wlan_ccmp, wlan_wep, altq, if_mib) are build-validated; module-only/netgraph/ipfw3/netsmb/vlan/sl/disc fixes apply cleanly to source (those subsystems are optional, not compiled into GENERIC).
Confirmed kernel references
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Detail
Exploit chain
none (false positive)
Evidence (decisive lines)
DF-0530 [NOT_REPRODUCED] - netgraph7/ng_fec.c:336
PoC changes
no code change (false positive) in findings/poc/DF-0530/
Verified recommended fix
No code change needed: false positive (counter correctly decremented at :336).
Verdict
FALSE POSITIVE: ng_fec_free_unit DOES decrement ng_units_in_use (ng_fec.c:336 ng_units_in_use--); the claimed double-increment does not exist.
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