Bug #76436 [NEW]: mysqli memory leak mysqli_fetch_object

From: luca dot looz92 at gmail dot com Operating system: centos 7 PHP version: 7.2.6 Package: MySQLi related Bug Type: Bug Bug description:mysqli memory leak mysqli_fetch_object Description: ------------ I was going crazy by investigating a memory issue on our server, php-fpm pools after a couple of days exhausts 16gb of RAM. By doing a lot of tests with trials and errors i was able to reproduce the issue. The memory leak happens when using functions like "mysqli_fetch_object" and "mysqli_fetch_array". Doesn't happen with "mysqli_fetch_row". I'm able to reproduce this by compiling php 7.2.6 from source with just the mysqli module: ./configure --disable-all --with-mysqli A very strange thing is that if I compile php in debug mode the leak doesn't happen anymore... ./configure --disable-all --enable-debug --with-mysqli If I put the code in a loop the leak doesn't become bigger so it seems that is limited per script execution by leaking something like 4 bytes for each execution. To test this I used the Wordpress default database by reading the hello world article. I have attached the valgrind results with "export ZEND_DONT_UNLOAD_MODULES=1". Another thing to note is that if set "export USE_ZEND_ALLOC=0" with the non-debug version the leak doesn't happen. I've seen this issue on 7.2.2, 7.2.5 and 7.2.6. Test script: --------------- <?php $dbh = mysqli_init(); mysqli_real_connect( $dbh, '127.0.0.1', 'root', 'mydbpass'); mysqli_select_db( $dbh, 'dbwpempty' ); $result = mysqli_query( $dbh, "SELECT * FROM wp_posts WHERE ID = 1 LIMIT 1" ); $num_rows = 0; $last_result = array(); while ( $row = mysqli_fetch_object( $result ) ) { $last_result[$num_rows] = $row; $num_rows++; } $result->free(); $dbh->close(); ?> valgrind --leak-check=full php mysqlleak.php Expected result: ---------------- ==30485== HEAP SUMMARY: ==30485== in use at exit: 32 bytes in 1 blocks ==30485== total heap usage: 10,515 allocs, 10,514 frees, 1,983,262 bytes allocated ==30485== ==30485== LEAK SUMMARY: ==30485== definitely lost: 0 bytes in 0 blocks ==30485== indirectly lost: 0 bytes in 0 blocks ==30485== possibly lost: 0 bytes in 0 blocks ==30485== still reachable: 32 bytes in 1 blocks ==30485== suppressed: 0 bytes in 0 blocks Actual result: -------------- ==30483== HEAP SUMMARY: ==30483== in use at exit: 936 bytes in 24 blocks ==30483== total heap usage: 9,275 allocs, 9,251 frees, 1,466,918 bytes allocated ==30483== ==30483== 904 bytes in 23 blocks are definitely lost in loss record 2 of 2 ==30483== at 0x4C29C23: malloc (vg_replace_malloc.c:299) ==30483== by 0x5B1198: __zend_malloc (zend_alloc.c:2829) ==30483== by 0x564684: zend_string_alloc (zend_string.h:134) ==30483== by 0x564684: zend_string_init (zend_string.h:170) ==30483== by 0x564684: php_mysqlnd_rset_field_read (mysqlnd_wireprotocol.c:1378) ==30483== by 0x56DA81: mysqlnd_mysqlnd_res_meta_read_metadata_pub (mysqlnd_result_meta.c:76) ==30483== by 0x56A2B6: mysqlnd_mysqlnd_res_read_result_metadata_pub (mysqlnd_result.c:385) ==30483== by 0x56C8D0: mysqlnd_query_read_result_set_header (mysqlnd_result.c:539) ==30483== by 0x55B152: mysqlnd_mysqlnd_conn_data_reap_query_pub (mysqlnd_connection.c:917) ==30483== by 0x55D79E: mysqlnd_mysqlnd_conn_data_query_pub (mysqlnd_connection.c:859) ==30483== by 0x4AA001: zif_mysqli_query (mysqli_nonapi.c:593) ==30483== by 0x671C93: ZEND_DO_ICALL_SPEC_RETVAL_USED_HANDLER (zend_vm_execute.h:617) ==30483== by 0x671C93: execute_ex (zend_vm_execute.h:59734) ==30483== by 0x67A690: zend_execute (zend_vm_execute.h:63760) ==30483== by 0x5D8FC7: zend_execute_scripts (zend.c:1496) ==30483== ==30483== LEAK SUMMARY: ==30483== definitely lost: 904 bytes in 23 blocks ==30483== indirectly lost: 0 bytes in 0 blocks ==30483== possibly lost: 0 bytes in 0 blocks ==30483== still reachable: 32 bytes in 1 blocks ==30483== suppressed: 0 bytes in 0 blocks ==30483== Reachable blocks (those to which a pointer was found) are not shown. -- Edit bug report at https://bugs.php.net/bug.php?id=76436&edit=1 -- Try a snapshot (PHP 5.4): https://bugs.php.net/fix.php?id=76436&r=trysnapshot54 Try a snapshot (PHP 5.5): https://bugs.php.net/fix.php?id=76436&r=trysnapshot55 Try a snapshot (trunk): https://bugs.php.net/fix.php?id=76436&r=trysnapshottrunk Fixed in SVN: https://bugs.php.net/fix.php?id=76436&r=fixed Fixed in release: https://bugs.php.net/fix.php?id=76436&r=alreadyfixed Need backtrace: https://bugs.php.net/fix.php?id=76436&r=needtrace Need Reproduce Script: https://bugs.php.net/fix.php?id=76436&r=needscript Try newer version: https://bugs.php.net/fix.php?id=76436&r=oldversion Not developer issue: https://bugs.php.net/fix.php?id=76436&r=support Expected behavior: https://bugs.php.net/fix.php?id=76436&r=notwrong Not enough info: https://bugs.php.net/fix.php?id=76436&r=notenoughinfo Submitted twice: https://bugs.php.net/fix.php?id=76436&r=submittedtwice register_globals: https://bugs.php.net/fix.php?id=76436&r=globals PHP 4 support discontinued: https://bugs.php.net/fix.php?id=76436&r=php4 Daylight Savings: https://bugs.php.net/fix.php?id=76436&r=dst IIS Stability: https://bugs.php.net/fix.php?id=76436&r=isapi Install GNU Sed: https://bugs.php.net/fix.php?id=76436&r=gnused Floating point limitations: https://bugs.php.net/fix.php?id=76436&r=float No Zend Extensions: https://bugs.php.net/fix.php?id=76436&r=nozend MySQL Configuration Error: https://bugs.php.net/fix.php?id=76436&r=mysqlcfg