Code: static void sas_eh_defer_cmd(struct scsi_cmnd *cmd)
{
	struct domain_device *dev = cmd_to_domain_dev(cmd);
	struct sas_ha_struct *ha = dev->port->ha;
	struct sas_task *task = TO_SAS_TASK(cmd);
	if (!dev_is_sata(dev)) {
		sas_eh_finish_cmd(cmd);
		return;
	}
	/* report the timeout to libata */
	sas_end_task(cmd, task);
	list_move_tail(&cmd->eh_entry, &ha->eh_ata_q);
}

Vulnerability Type: DoS 
CWE ID: 
Summary: ** DISPUTED ** drivers/scsi/libsas/sas_scsi_host.c in the Linux kernel before 4.16 allows local users to cause a denial of service (ata qc leak) by triggering certain failure conditions. NOTE: a third party disputes the relevance of this report because the failure can only occur for physically proximate attackers who unplug SAS Host Bus Adapter cables.
Commit Message: scsi: libsas: defer ata device eh commands to libata

When ata device doing EH, some commands still attached with tasks are
not passed to libata when abort failed or recover failed, so libata did
not handle these commands. After these commands done, sas task is freed,
but ata qc is not freed. This will cause ata qc leak and trigger a
warning like below:

WARNING: CPU: 0 PID: 28512 at drivers/ata/libata-eh.c:4037
ata_eh_finish+0xb4/0xcc
CPU: 0 PID: 28512 Comm: kworker/u32:2 Tainted: G     W  OE 4.14.0#1
......
Call trace:
[<ffff0000088b7bd0>] ata_eh_finish+0xb4/0xcc
[<ffff0000088b8420>] ata_do_eh+0xc4/0xd8
[<ffff0000088b8478>] ata_std_error_handler+0x44/0x8c
[<ffff0000088b8068>] ata_scsi_port_error_handler+0x480/0x694
[<ffff000008875fc4>] async_sas_ata_eh+0x4c/0x80
[<ffff0000080f6be8>] async_run_entry_fn+0x4c/0x170
[<ffff0000080ebd70>] process_one_work+0x144/0x390
[<ffff0000080ec100>] worker_thread+0x144/0x418
[<ffff0000080f2c98>] kthread+0x10c/0x138
[<ffff0000080855dc>] ret_from_fork+0x10/0x18

If ata qc leaked too many, ata tag allocation will fail and io blocked
for ever.

As suggested by Dan Williams, defer ata device commands to libata and
merge sas_eh_finish_cmd() with sas_eh_defer_cmd(). libata will handle
ata qcs correctly after this.

Signed-off-by: Jason Yan <yanaijie@huawei.com>
CC: Xiaofei Tan <tanxiaofei@huawei.com>
CC: John Garry <john.garry@huawei.com>
CC: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>