Commit eddb98ad authored Feb 20, 2026 by Damien Le Moal

ata: libata-eh: correctly handle deferred qc timeouts



A deferred qc may timeout while waiting for the device queue to drain
to be submitted. In such case, since the qc is not active,
ata_scsi_cmd_error_handler() ends up calling scsi_eh_finish_cmd(),
which frees the qc. But as the port deferred_qc field still references
this finished/freed qc, the deferred qc work may eventually attempt to
call ata_qc_issue() against this invalid qc, leading to errors such as
reported by UBSAN (syzbot run):

UBSAN: shift-out-of-bounds in drivers/ata/libata-core.c:5166:24
shift exponent 4210818301 is too large for 64-bit type 'long long unsigned int'
...
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 ubsan_epilogue+0xa/0x30 lib/ubsan.c:233
 __ubsan_handle_shift_out_of_bounds+0x279/0x2a0 lib/ubsan.c:494
 ata_qc_issue.cold+0x38/0x9f drivers/ata/libata-core.c:5166
 ata_scsi_deferred_qc_work+0x154/0x1f0 drivers/ata/libata-scsi.c:1679
 process_one_work+0x9d7/0x1920 kernel/workqueue.c:3275
 process_scheduled_works kernel/workqueue.c:3358 [inline]
 worker_thread+0x5da/0xe40 kernel/workqueue.c:3439
 kthread+0x370/0x450 kernel/kthread.c:467
 ret_from_fork+0x754/0xd80 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

Fix this by checking if the qc of a timed out SCSI command is a deferred
one, and in such case, clear the port deferred_qc field and finish the
SCSI command with DID_TIME_OUT.

Reported-by:  <syzbot+1f77b8ca15336fff21ff@syzkaller.appspotmail.com>
Fixes: 0ea84089 ("ata: libata-scsi: avoid Non-NCQ command starvation")
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Igor Pylypiv <ipylypiv@google.com>

parent 6de23f81

drivers/ata/libata-eh.c

+19 −3

Original line number	Diff line number	Diff line
		@@ -640,12 +640,28 @@ void ata_scsi_cmd_error_handler(struct Scsi_Host host, struct ata_port ap,
		set_host_byte(scmd, DID_OK);

		ata_qc_for_each_raw(ap, qc, i) {
		if (qc->flags & ATA_QCFLAG_ACTIVE &&
		qc->scsicmd == scmd)
		if (qc->scsicmd != scmd)
		continue;
		if ((qc->flags & ATA_QCFLAG_ACTIVE) \|\|
		qc == ap->deferred_qc)
		break;
		}

		if (i < ATA_MAX_QUEUE) {
		if (qc == ap->deferred_qc) {
		/*
		* This is a deferred command that timed out while
		* waiting for the command queue to drain. Since the qc
		* is not active yet (deferred_qc is still set, so the
		* deferred qc work has not issued the command yet),
		* simply signal the timeout by finishing the SCSI
		* command and clear the deferred qc to prevent the
		* deferred qc work from issuing this qc.
		*/
		WARN_ON_ONCE(qc->flags & ATA_QCFLAG_ACTIVE);
		ap->deferred_qc = NULL;
		set_host_byte(scmd, DID_TIME_OUT);
		scsi_eh_finish_cmd(scmd, &ap->eh_done_q);
		} else if (i < ATA_MAX_QUEUE) {
		/* the scmd has an associated qc */
		if (!(qc->flags & ATA_QCFLAG_EH)) {
		/* which hasn't failed yet, timeout */