target: Reject SCSI data overflow for fabrics using transport_generic_map_mem_to_cmd

This patch changes transport_generic_map_mem_to_cmd() to reject SCSI data
overflow and to send exception status with CHECK_CONDITION + TCM_INVALID_CDB_FIELD
for fabrics that are passing a pre-populated struct scatterlist (eg: tcm_loop
and iscsi-target) being mapped into se_cmd->t_data_sg and se_cmd->t_data_nents.

This addresses an OOPs where transport_allocate_data_tasks() would walk
the incorrect post OVERFLOW cmd->data_length value beyond the end of
the passed scatterlist.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Andy Grover <agrover@redhat.com>
Cc: stable@kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_transport.c

@@ -3411,6 +3411,18 @@ int transport_generic_map_mem_to_cmd(
 
 	if ((cmd->se_cmd_flags & SCF_SCSI_DATA_SG_IO_CDB) ||
 	    (cmd->se_cmd_flags & SCF_SCSI_CONTROL_SG_IO_CDB)) {
+		/*
+		 * Reject SCSI data overflow with map_mem_to_cmd() as incoming
+		 * scatterlists already have been set to follow what the fabric
+		 * passes for the original expected data transfer length.
+		 */
+		if (cmd->se_cmd_flags & SCF_OVERFLOW_BIT) {
+			pr_warn("Rejecting SCSI DATA overflow for fabric using"
+				" SCF_PASSTHROUGH_SG_TO_MEM_NOALLOC\n");
+			cmd->se_cmd_flags |= SCF_SCSI_CDB_EXCEPTION;
+			cmd->scsi_sense_reason = TCM_INVALID_CDB_FIELD;
+			return -EINVAL;
+		}
 
 		cmd->t_data_sg = sgl;
 		cmd->t_data_nents = sgl_count;