InnoDB bug fix: mem_realloc() didn't preserve the block contents

innobase/include/mem0mem.ic

@@ -575,9 +575,21 @@ mem_realloc(
 	char*  	file_name,/* in: file name where called */
 	ulint 	line)  	/* in: line where called */
 {
+	mem_heap_t*	heap = (mem_heap_t*)((byte*)buf
+			- MEM_BLOCK_HEADER_SIZE - MEM_FIELD_HEADER_SIZE);
+	ulint		size;
+	ut_a(heap->magic_n == MEM_BLOCK_MAGIC_N);
+	size = mem_block_get_len(heap);
+	ut_a(size > MEM_BLOCK_HEADER_SIZE + MEM_FIELD_HEADER_SIZE);
+	size -= MEM_BLOCK_HEADER_SIZE + MEM_FIELD_HEADER_SIZE;
+
+	if (n > size) {
+		void*	newbuf = memcpy(mem_alloc_func(n, file_name, line),
+					buf, size);
 		mem_free(buf);
-
-	return(mem_alloc_func(n, file_name, line));
+		buf = newbuf;
+	}
+	return(buf);
 }
 
 /**************************************************************************