Fixed bug #80761

When row data split across multiple packets, allocate a temporary
buffer that can be reallocated, and only copy into the row buffer
pool arena once we know the final size. This avoids quadratic
memory usage for very large results.

(cherry picked from commit 1fc4c89)

Author: nikic

NEWS

@@ -13,6 +13,9 @@ PHP                                                                        NEWS
     reference). (Dmitry)
   . Fixed bug #80968 (JIT segfault with return from required file). (Dmitry)
 
+- MySQLnd:
+  . Fixed bug #80761 (PDO uses too much memory). (Nikita)
+
 - Standard:
   . Fixed bug #81048 (phpinfo(INFO_VARIABLES) "Array to string conversion").
     (cmb)

ext/mysqlnd/mysqlnd_wireprotocol.c

@@ -1391,47 +1391,39 @@ php_mysqlnd_read_row_ex(MYSQLND_PFC * pfc,
 		SET_CONNECTION_STATE(connection_state, CONN_QUIT_SENT);
 		set_packet_error(error_info, CR_SERVER_GONE_ERROR, UNKNOWN_SQLSTATE, mysqlnd_server_gone);
 	} else {
+		/* If the packet is split in multiple chunks, allocate a temporary buffer that we can
+		 * reallocate, and only afterwards copy it to the pool when we know the final size. */
+		zend_uchar *buf = NULL;
+		while (header.size >= MYSQLND_MAX_PACKET_SIZE) {
+			buf = erealloc(buf, *data_size + header.size);
+			p = buf + *data_size;
+			*data_size += header.size;
+
+			if (UNEXPECTED(PASS != (ret = pfc->data->m.receive(pfc, vio, p, header.size, stats, error_info)))) {
+				DBG_ERR("Empty row packet body");
+				SET_CONNECTION_STATE(connection_state, CONN_QUIT_SENT);
+				set_packet_error(error_info, CR_SERVER_GONE_ERROR, UNKNOWN_SQLSTATE, mysqlnd_server_gone);
+				efree(buf);
+				DBG_RETURN(FAIL);
+			}
+			if (FAIL == mysqlnd_read_header(pfc, vio, &header, stats, error_info)) {
+				efree(buf);
+				DBG_RETURN(FAIL);
+			}
+		}
+
+		buffer->ptr = pool->get_chunk(pool, *data_size + header.size + prealloc_more_bytes);
+		if (buf) {
+			memcpy(buffer->ptr, buf, *data_size);
+			efree(buf);
+		}
+		p = (zend_uchar *) buffer->ptr + *data_size;
 		*data_size += header.size;
-		buffer->ptr = pool->get_chunk(pool, *data_size + prealloc_more_bytes);
-		p = buffer->ptr;
 
 		if (UNEXPECTED(PASS != (ret = pfc->data->m.receive(pfc, vio, p, header.size, stats, error_info)))) {
 			DBG_ERR("Empty row packet body");
 			SET_CONNECTION_STATE(connection_state, CONN_QUIT_SENT);
 			set_packet_error(error_info, CR_SERVER_GONE_ERROR, UNKNOWN_SQLSTATE, mysqlnd_server_gone);
-		} else {
-			while (header.size >= MYSQLND_MAX_PACKET_SIZE) {
-				if (FAIL == mysqlnd_read_header(pfc, vio, &header, stats, error_info)) {
-					ret = FAIL;
-					break;
-				}
-
-				*data_size += header.size;
-
-				/* Empty packet after MYSQLND_MAX_PACKET_SIZE packet. That's ok, break */
-				if (!header.size) {
-					break;
-				}
-
-				/*
-				  We have to realloc the buffer.
-				*/
-				buffer->ptr = pool->resize_chunk(pool, buffer->ptr, *data_size - header.size, *data_size + prealloc_more_bytes);
-				if (!buffer->ptr) {
-					SET_OOM_ERROR(error_info);
-					ret = FAIL;
-					break;
-				}
-				/* The position could have changed, recalculate */
-				p = (zend_uchar *) buffer->ptr + (*data_size - header.size);
-
-				if (PASS != (ret = pfc->data->m.receive(pfc, vio, p, header.size, stats, error_info))) {
-					DBG_ERR("Empty row packet body");
-					SET_CONNECTION_STATE(connection_state, CONN_QUIT_SENT);
-					set_packet_error(error_info, CR_SERVER_GONE_ERROR, UNKNOWN_SQLSTATE, mysqlnd_server_gone);
-					break;
-				}
-			}
 		}
 	}
 	if (ret == FAIL && buffer->ptr) {