Fix for bug#51875/#11759554 backported from mysql-5.1.

mysql-test/r/gis.result

@@ -996,4 +996,11 @@ ERROR 42000: You have an error in your SQL syntax; check the manual that corresp
 ALTER TABLE t2 ADD SPATIAL INDEX USING BTREE (col1);
 ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'USING BTREE (col1)' at line 1
 DROP TABLE t2;
+#
+# BUG#51875: crash when loading data into geometry function polyfromwkb
+#
+SET @a=0x00000000030000000100000000000000000000000000144000000000000014400000000000001840000000000000184000000000000014400000000000001440;
+SET @a=POLYFROMWKB(@a);
+SET @a=0x00000000030000000000000000000000000000000000144000000000000014400000000000001840000000000000184000000000000014400000000000001440;
+SET @a=POLYFROMWKB(@a);
 End of 5.0 tests

mysql-test/t/gis.test

@@ -685,4 +685,14 @@ ALTER TABLE t2 ADD SPATIAL INDEX USING BTREE (col1);
 
 DROP TABLE t2;
 
+
+--echo #
+--echo # BUG#51875: crash when loading data into geometry function polyfromwkb
+--echo #
+SET @a=0x00000000030000000100000000000000000000000000144000000000000014400000000000001840000000000000184000000000000014400000000000001440;
+SET @a=POLYFROMWKB(@a);
+SET @a=0x00000000030000000000000000000000000000000000144000000000000014400000000000001840000000000000184000000000000014400000000000001440;
+SET @a=POLYFROMWKB(@a);
+
+
 --echo End of 5.0 tests

sql/spatial.cc

@@ -519,7 +519,7 @@ uint Gis_line_string::init_from_wkb(const char *wkb, uint len,
   n_points= wkb_get_uint(wkb, bo);
   proper_length= 4 + n_points * POINT_DATA_SIZE;
 
-  if (len < proper_length || res->reserve(proper_length))
+  if (!n_points || len < proper_length || res->reserve(proper_length))
     return 0;
 
   res->q_append(n_points);
@@ -737,7 +737,9 @@ uint Gis_polygon::init_from_wkb(const char *wkb, uint len, wkbByteOrder bo,
   if (len < 4)
     return 0;
 
-  n_linear_rings= wkb_get_uint(wkb, bo);
+  if (!(n_linear_rings= wkb_get_uint(wkb, bo)))
+    return 0;
+
   if (res->reserve(4, 512))
     return 0;
   wkb+= 4;