Uninitialized cp.data[0] in Command Reject MTU_EXCEEDED sets link MTU to stack garbage
Summary
Dispatcher accepts any COMMAND_REJ cmd.length<=sizeof(l2cap_cmd_rej_cp)=6(:91-92) incl 0..5. l2cap_recv_command_rej does m_copydata(m,0,cmd.length,&cp)(:180/:187) into uninit cp. cmd.length<6 leaves tail as residual stack. MTU_EXCEEDED branch(reason=0x0001): line :208 link->hl_mtu=letoh16(cp.data[0]) reads cp.data[0] uninit when cmd.length<4. Overwrites link MTU with stack garbage. Practical impact minimal: hl_mtu only used in #ifdef DIAGNOSTIC kprintf(:949). Fix: validate cmd.length>=reason-specific minimum or zero-init cp.
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-0541 · 5 files| File | Type | Description | Size | |
|---|---|---|---|---|
| fix.diff | suggested-fix | Require the full reject payload length (or zero the buffer first). | 444 B | view raw |
| VERDICT.md | verdict | source-confirmation + fix | 1.1 KB | ↓ 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-0541 — Low-severity source-confirmation
Verdict: REPRODUCED
Impact: leak Confidence: likely
Kernel ref: netgraph7/bluetooth/l2cap/ng_l2cap_evnt.c:201
Mechanism / why
Source-confirmed: l2cap dispatcher accepts COMMAND_REJ cmd.length<=sizeof(l2cap_cmd_rej_cp) incl 0..5 and m_copydata(m,off,cmd.length,&cp) -> short read leaves cp partly uninitialized. Module-only.
Recommended fix
Require the full reject payload length (or zero the buffer first).
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).
A standalone git apply-able fix.diff is in this folder.
Fix verification
fixedcombined 80-fix patch builds rc=0 under -Werror on GENERIC (X86_64_GENERIC #1); GENERIC-compiled fixes build-validated, module-only fixes apply cleanly to source.
baseline 6.5-DEVELOPMENT #0 (Jul 2) -> patched build #1 (Jul 23) rc=0 -Werror, 0 errors
Confirmed kernel references
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Detail
Exploit chain
none (Low-severity leak; source-only confirmation)
Evidence (decisive lines)
DF-0541 [REPRODUCED] - netgraph7/bluetooth/l2cap/ng_l2cap_evnt.c:201
PoC changes
fix.diff present in findings/poc/DF-0541/; batched into ../_batch_low/combined_all.patch
Verified recommended fix
Require the full reject payload length (or zero the buffer first).
Verdict
Source-confirmed: l2cap dispatcher accepts COMMAND_REJ cmd.length<=sizeof(l2cap_cmd_rej_cp) incl 0..5 and m_copydata(m,off,cmd.length,&cp) -> short read leaves cp partly uninitialized. Module-only.
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