MDEV-19660: wsrep_rec_get_foreign_key() is dereferencing a stale pointer to a page that was previously latched

In row_ins_foreign_check_on_constraint(), clustered index record is being passed to wsrep_append_foreign_key() after releasing the latch. If a record has been changed by other thread in the meantime then it could lead to a crash when
wsrep_rec_get_foreign_key () tries to access the record.

row_ins_foreign_check_on_constraint
	Use cascade->pcur->old_rec instead of clust_rec.

row_ins_check_foreign_constraint
	Add missing error printout.

Author: Jan Lindström

storage/innobase/row/row0ins.cc

@@ -1293,7 +1293,7 @@ row_ins_foreign_check_on_constraint(
 	err = wsrep_append_foreign_key(
 				       thr_get_trx(thr),
 				       foreign,
-				       clust_rec,
+				       cascade->pcur->old_rec,
 				       clust_index,
 				       FALSE, WSREP_KEY_EXCLUSIVE);
 	if (err != DB_SUCCESS) {
@@ -1664,6 +1664,11 @@ row_ins_check_foreign_constraint(
 						check_index,
 						check_ref,
 						key_type);
+
+					if (err != DB_SUCCESS) {
+						fprintf(stderr,
+							"WSREP: foreign key append failed: %d\n", err);
+					}
 #endif /* WITH_WSREP */
 					goto end_scan;
 				} else if (foreign->type != 0) {

storage/xtradb/row/row0ins.cc

@@ -1299,7 +1299,7 @@ row_ins_foreign_check_on_constraint(
 	err = wsrep_append_foreign_key(
 				       thr_get_trx(thr),
 				       foreign,
-				       clust_rec,
+				       cascade->pcur->old_rec,
 				       clust_index,
 				       FALSE, WSREP_KEY_EXCLUSIVE);
 	if (err != DB_SUCCESS) {
@@ -1676,6 +1676,11 @@ row_ins_check_foreign_constraint(
 						check_index,
 						check_ref,
 						key_type);
+
+					if (err != DB_SUCCESS) {
+						fprintf(stderr,
+							"WSREP: foreign key append failed: %d\n", err);
+					}
 #endif /* WITH_WSREP */
 					goto end_scan;
 				} else if (foreign->type != 0) {