target: Check number of unmap descriptors against our limit

Fail UNMAP commands that have more than our reported limit on unmap
descriptors.
Signed-off-by: Roland Dreier <roland@purestorage.com>
Cc: stable@vger.kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_iblock.c

@@ -336,6 +336,11 @@ static int iblock_execute_unmap(struct se_cmd *cmd)
 	bd_dl = get_unaligned_be16(&buf[2]);
 
 	size = min(size - 8, bd_dl);
+	if (size / 16 > dev->se_sub_dev->se_dev_attrib.max_unmap_block_desc_count) {
+		cmd->scsi_sense_reason = TCM_INVALID_PARAMETER_LIST;
+		ret = -EINVAL;
+		goto err;
+	}
 
 	/* First UNMAP block descriptor starts at 8 byte offset */
 	ptr = &buf[8];