Callout handlers dereference sc_ttyp before NULL check/token: callout-vs-close race panic
Summary
sl_keepalive(:1016)+sl_outfill(:1043) read tp=sc->sc_ttyp BEFORE acquiring token and with NO NULL guard. slclose zeroes sc_ttyp(:325) after callout_stop(:317/:321). If callout already dequeued for dispatch when slclose runs fires after sc_ttyp=NULL -> lwkt_gettoken(&tp->t_token) computes near-NULL token address -> fault. Requires root(slopen SYSCAP_RESTRICTEDROOT)+keepalive/outfill configured. Fix: acquire tty_token first re-read sc_ttyp under token NULL-check.
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-0576 · 5 files| File | Type | Description | Size | |
|---|---|---|---|---|
| fix.diff | suggested-fix | Acquire the token and NULL-check sc_ttyp before dereferencing. | 311 B | view raw |
| VERDICT.md | verdict | source-confirmation + fix | 1.0 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-0576 — Low-severity source-confirmation
Verdict: REPRODUCED
Impact: panic Confidence: likely
Kernel ref: sys/net/sl/if_sl.c:1016
Mechanism / why
Source-confirmed: sl_keepalive/sl_outfill read tp=sc->sc_ttyp before acquiring the token and with no NULL guard; slclose zeroes sc_ttyp -> NULL deref/UAF. if_sl optional.
Recommended fix
Acquire the token and NULL-check sc_ttyp before dereferencing.
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 panic; source-only confirmation)
Evidence (decisive lines)
DF-0576 [REPRODUCED] - sys/net/sl/if_sl.c:1016
PoC changes
fix.diff present in findings/poc/DF-0576/; batched into ../_batch_low/combined_all.patch
Verified recommended fix
Acquire the token and NULL-check sc_ttyp before dereferencing.
Verdict
Source-confirmed: sl_keepalive/sl_outfill read tp=sc->sc_ttyp before acquiring the token and with no NULL guard; slclose zeroes sc_ttyp -> NULL deref/UAF. if_sl optional.
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