target: bounds check XCOPY segment descriptor list

Check the length of the XCOPY request segment descriptor list against
the value advertised via the MAXIMUM SEGMENT DESCRIPTOR COUNT field in
the RECEIVE COPY OPERATING PARAMETERS response.

spc4r37 6.4.3.5 states:
  If the number of segment descriptors exceeds the allowed number, the
  copy manager shall terminate the command with CHECK CONDITION status,
  with the sense key set to ILLEGAL REQUEST, and the additional sense
  code set to TOO MANY SEGMENT DESCRIPTORS.

This functionality is testable using the libiscsi
ExtendedCopy.DescrLimits test.
Signed-off-by: David Disseldorp <ddiss@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>

drivers/target/target_core_xcopy.c

@@ -308,17 +308,26 @@ static int target_xcopy_parse_segdesc_02(struct se_cmd *se_cmd, struct xcopy_op
 
 static int target_xcopy_parse_segment_descriptors(struct se_cmd *se_cmd,
 				struct xcopy_op *xop, unsigned char *p,
-				unsigned int sdll)
+				unsigned int sdll, sense_reason_t *sense_ret)
 {
 	unsigned char *desc = p;
 	unsigned int start = 0;
 	int offset = sdll % XCOPY_SEGMENT_DESC_LEN, rc, ret = 0;
 
+	*sense_ret = TCM_INVALID_PARAMETER_LIST;
+
 	if (offset != 0) {
 		pr_err("XCOPY segment descriptor list length is not"
 			" multiple of %d\n", XCOPY_SEGMENT_DESC_LEN);
 		return -EINVAL;
 	}
+	if (sdll > RCR_OP_MAX_SG_DESC_COUNT * XCOPY_SEGMENT_DESC_LEN) {
+		pr_err("XCOPY supports %u segment descriptor(s), sdll: %u too"
+			" large..\n", RCR_OP_MAX_SG_DESC_COUNT, sdll);
+		/* spc4r37 6.4.3.5 SEGMENT DESCRIPTOR LIST LENGTH field */
+		*sense_ret = TCM_TOO_MANY_SEGMENT_DESCS;
+		return -EINVAL;
+	}
 
 	while (start < sdll) {
 		/*
@@ -916,7 +925,8 @@ sense_reason_t target_do_xcopy(struct se_cmd *se_cmd)
 	seg_desc = &p[16];
 	seg_desc += (rc * XCOPY_TARGET_DESC_LEN);
 
-	rc = target_xcopy_parse_segment_descriptors(se_cmd, xop, seg_desc, sdll);
+	rc = target_xcopy_parse_segment_descriptors(se_cmd, xop, seg_desc,
+						    sdll, &ret);
 	if (rc <= 0) {
 		xcopy_pt_undepend_remotedev(xop);
 		goto out;