target: Add workaround for zero-length control CDB handling

This patch adds a work-around for handling zero allocation length
control CDBs (type SCF_SCSI_CONTROL_SG_IO_CDB) that was causing an
OOPs with the following raw calls:

   # sg_raw -v /dev/sdd 3 0 0 0 0 0
   # sg_raw -v /dev/sdd 0x1a 0 1 0 0 0

This patch will follow existing zero-length handling for data I/O
and silently return with GOOD status.  This addresses the zero length
issue, but the proper long-term resolution for handling arbitary
allocation lengths will be to refactor out data-phase handling in
individual CDB emulation logic within target_core_cdb.c

Reported-by: Roland Dreier <roland@purestorage.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_transport.c

@@ -3759,6 +3759,11 @@ transport_allocate_control_task(struct se_cmd *cmd)
 	struct se_task *task;
 	unsigned long flags;
 
+	/* Workaround for handling zero-length control CDBs */
+	if ((cmd->se_cmd_flags & SCF_SCSI_CONTROL_SG_IO_CDB) &&
+	    !cmd->data_length)
+		return 0;
+
 	task = transport_generic_get_task(cmd, cmd->data_direction);
 	if (!task)
 		return -ENOMEM;
@@ -3830,6 +3835,14 @@ int transport_generic_new_cmd(struct se_cmd *cmd)
 	else if (!task_cdbs && (cmd->se_cmd_flags & SCF_SCSI_DATA_SG_IO_CDB)) {
 		cmd->t_state = TRANSPORT_COMPLETE;
 		atomic_set(&cmd->t_transport_active, 1);
+
+		if (cmd->t_task_cdb[0] == REQUEST_SENSE) {
+			u8 ua_asc = 0, ua_ascq = 0;
+
+			core_scsi3_ua_clear_for_request_sense(cmd,
+					&ua_asc, &ua_ascq);
+		}
+
 		INIT_WORK(&cmd->work, target_complete_ok_work);
 		queue_work(target_completion_wq, &cmd->work);
 		return 0;