CVE-2026-23355

In the Linux kernel, the following vulnerability has been resolved:

ata: libata: cancel pending work after clearing deferred_qc

Syzbot reported a WARN_ON() in ata_scsi_deferred_qc_work(), caused by

ap->ops->qc_defer() returning non-zero before issuing the deferred qc.

ata_scsi_schedule_deferred_qc() is called during each command completion.

This function will check if there is a deferred QC, and if

ap->ops->qc_defer() returns zero, meaning that it is possible to queue the

deferred qc at this time (without being deferred), then it will queue the

work which will issue the deferred qc.

Once the work get to run, which can potentially be a very long time after

the work was scheduled, there is a WARN_ON() if ap->ops->qc_defer() returns

non-zero.

While we hold the ap->lock both when assigning and clearing deferred_qc,

and the work itself holds the ap->lock, the code currently does not cancel

the work after clearing the deferred qc.

This means that the following scenario can happen:

1) One or several NCQ commands are queued.

2) A non-NCQ command is queued, gets stored in ap->deferred_qc.

3) Last NCQ command gets completed, work is queued to issue the deferred

qc.

4) Timeout or error happens, ap->deferred_qc is cleared. The queued work is

currently NOT canceled.

5) Port is reset.

6) One or several NCQ commands are queued.

7) A non-NCQ command is queued, gets stored in ap->deferred_qc.

8) Work is finally run. Yet at this time, there is still NCQ commands in

flight.

The work in 8) really belongs to the non-NCQ command in 2), not to the

non-NCQ command in 7). The reason why the work is executed when it is not

supposed to, is because it was never canceled when ap->deferred_qc was

cleared in 4). Thus, ensure that we always cancel the work after clearing

ap->deferred_qc.

Another potential fix would have been to let ata_scsi_deferred_qc_work() do

nothing if ap->ops->qc_defer() returns non-zero. However, canceling the

work when clearing ap->deferred_qc seems slightly more logical, as we hold

the ap->lock when clearing ap->deferred_qc, so we know that the work cannot

be holding the lock. (The function could be waiting for the lock, but that

is okay since it will do nothing if ap->deferred_qc is not set.)