ata-queue: ata_fail_requests leaks controller serialization lock when failing running request
Summary
ata_fail_requests at 577-582 fails ch->running: callout_cancel; ch->running=NULL; request->result=ENXIO; TAILQ_INSERT_TAIL. NO ATA_LOCKING(dev, ATA_LF_UNLOCK) called. Every other path clearing ch->running releases this lock: ata_interrupt ata-all.c:353-357, ata_timeout 555-561, ata_start 251-255, ata_reinit ata-all.c:207-262. ata_start at 227 acquired lock with ATA_LOCKING(LF_LOCK). On controllers with real serialize (ata-acard.c:76 ctlr->locking=ata_serialize) serial->locked_ch=ch->unit permanently blocks sibling channels ata_serialize (ata-acard.c:229-234) returns locked_ch for every sibling LF_LOCK. Trigger: root IOCATADETACH during in-flight I/O or physical hot-unplug. Controller-wide I/O hang for system lifetime. Pure DoS no memory corruption.
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-1752 · 2 files| File | Type | Description | Size | |
|---|---|---|---|---|
| fix.diff | suggested-fix | Call ATA_LOCKING(dev, ATA_LF_UNLOCK) when clearing ch->running. | 421 B | view raw |
| VERDICT.md | verdict | full analysis | 1.1 KB | ↓ raw |
DF-1752 — Verdict
Severity: Low Status: REPRODUCED (source-only confirmation — driver/HW-gated, not runtime-triggered on QEMU guest) Impact: dos Confidence: certain
Verdict
REPRODUCED. The cited bug is confirmed real in the audited source at sys/dev/disk/nata/ata-queue.c:577-582.
Mechanism
ata_fail_requests clears ch->running without releasing the serialization lock (ATA_LOCKING LF_UNLOCK); permanently blocks sibling channels on serialize controllers.
Fix
Call ATA_LOCKING(dev, ATA_LF_UNLOCK) when clearing ch->running.
The full git-apply-able diff is in fix.diff.
Build validation
fix.diff applies cleanly and compiles with -Werror as part of the batch module build
(all 51 fixes applied to /usr/src, kernel+modules built).
Notes
Source-only confirmation: this finding is in a device driver code path that requires specific hardware not present in the QEMU guest. The bug is confirmed by source tracing (cited path:line verified against sys/), and the fix compiles clean. No runtime trigger was attempted as the relevant device/module is HW-gated.
Fix verification
fixedVALIDATED via batch build rc=0.
nata module built with -Werror.
Confirmed kernel references
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Detail
Exploit chain
none
Evidence (decisive lines)
Source traced at sys/dev/disk/nata/ata-queue.c:577-582. Fix compiled clean.
PoC changes
authored fix.diff: add ATA_LOCKING LF_UNLOCK when clearing running
Verified recommended fix
Release serialization lock when clearing ch->running. Matches finding proposal.
Verdict
REPRODUCED (source-only). ata_fail_requests clears ch->running without ATA_LOCKING LF_UNLOCK; permanently blocks sibling channels on serialize controllers.
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