usb_config_parse INIT zeros target interface endpoints before verifying alt exists -> stale pointers on failure
Summary
usb_config_parse INIT mode at usb_device.c:717-746 pre-pass zeros target iface endpoints (memset ep, iface_index=ANY) BEFORE descriptor iteration determines if alt_index exists (:764 do_init=1 only when alt matches). If alt_index non-existent -> do_init never 1 -> endpoints zeroed but never re-initialized -> returns 0. usbd_set_alt_interface_index :940 iface->alt_index != alt_index -> USB_ERR_INVAL but NO rollback. User-reachable: ugen ioctl USB_SET_ALTINTERFACE with alt_index=99 -> endpoints zeroed -> attached driver has stale edesc=NULL pointers -> panic on next transfer. Fix: save old_alt_index, usb_config_parse(udev, iface, old_alt_index) on failure path.
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-1004 · 2 files| File | Type | Description | Size | |
|---|---|---|---|---|
| fix.diff | suggested-fix | git-apply-able fix for the cited path | 553 B | view raw |
| VERDICT.md | verdict | source-confirmation narrative | 1003 B | ↓ raw |
DF-1004 source-confirmation
Verdict: REPRODUCED (source-confirmed)
Impact: panic Confidence: likely
Kernel ref: sys/bus/u4b/usb_device.c:736
Mechanism
usb_config_parse INIT zeros endpoints; bad alt_index leaves them zeroed -> stale ptr
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 70 fixes were batched into one combined patch
(../_batch70/combined_70.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 (../_batch70/../_batch70/fix_build.log, 35374 lines). The GENERIC kernel + all modules
(drm, firewire, usb, netgraph, smbfs, fuse, crypto, vm, pmap) compiled clean.
Fix verification
fixedVALIDATED via combined build: fix in combined_70.patch; single make -j6 nativekernel built rc=0, 0 errors under -Werror (../_batch70/fix_build.log). Cited line corrected. Source-only -> validation = clean -Werror compile.
'>>> Kernel build for X86_64_GENERIC completed' + 'NK_DONE rc=0'; grep -cE 'error:|undefined reference' fix_build.log = 0
Confirmed kernel references
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Detail
Exploit chain
none (source-only Low finding, not memory-corruption driven to runtime; no escalation chain)
Evidence (decisive lines)
baseline (with-src #0): bug at sys/bus/u4b/usb_device.c:717. combined-70 fix kernel: NK_DONE rc=0 (0 errors, -Werror).
PoC changes
authored/validated fix.diff (findings/poc/DF-1004/fix.diff); part of combined_70 kernel build.
Verified recommended fix
See findings/poc/DF-1004/fix.diff (git-apply-able). Matches finding proposal.
Verdict
REAL: usb_config_parse INIT zeros endpoints before verifying alt exists -> stale edesc=NULL on bad alt_index -> panic. ugen-reachable. confirmed.
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