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Bug #71023 mysqlnd statistic wrap
Submitted: 2015-12-04 05:41 UTC Modified: 2021-08-05 13:35 UTC
Votes:5
Avg. Score:3.8 ± 1.0
Reproduced:4 of 5 (80.0%)
Same Version:1 (25.0%)
Same OS:0 (0.0%)
From: damian dot poole at netregistry dot com dot au Assigned:
Status: Verified Package: MySQL related
PHP Version: 7.0.0 OS: Debian x86_64
Private report: No CVE-ID: None
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 [2015-12-04 05:41 UTC] damian dot poole at netregistry dot com dot au 
Description:
------------
Some of the connection statistics for the MySQL native driver (namely active_connections/ active persistent connections) can decrement past zero causing the statistic to wrap around to the max value of the type.

The attached patch fixes it for us as it stops the macros which increment/decrement from wrapping around.

Test script:
---------------
<?php
$mysqli = mysqli_init();
$mysqli->real_connect('1.2.3.4'); //non existant server
$stats = mysqli_get_client_stats();
var_dump($stats['active_connections']);

Expected result:
----------------
Warning: mysqli::real_connect(): (HY000/2002): Connection refused in /websites/ph/php70.damo.id.au/mysql.php on line 3
string(2) "0"

--- next run ---
Warning: mysqli::real_connect(): (HY000/2002): Connection refused in /websites/ph/php70.damo.id.au/mysql.php on line 3
string(2) "0"

Actual result:
--------------
Warning: mysqli::real_connect(): (HY000/2002): Connection refused in /websites/ph/php70.damo.id.au/mysql.php on line 3
string(20) "18446744073709551615"

--- next run ---
Warning: mysqli::real_connect(): (HY000/2002): Connection refused in /websites/ph/php70.damo.id.au/mysql.php on line 3
string(20) "18446744073709551614"

Patches

dpoole-nowrap-for-mysqlnd-uint64-decrement-or-increment (last revision 2015-12-04 05:46 UTC by damian dot poole at netregistry dot com dot au)
dpoole-nowrap-for-mysqlnd-uint64 (last revision 2015-12-04 05:41 UTC by damian dot poole at netregistry dot com dot au)

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 [2021-08-05 13:35 UTC] cmb@php.net
-Status: Open +Status: Verified
 [2021-08-05 13:35 UTC] cmb@php.net 
I can confirm the erroneous behavior.  Thank you for the patch;
however, it doesn't look quite right to me.  What happens if there
is one connection open, and someone attempts to connect to a
non-existing server?  Wouldn't the active_connections be reported
as 0 afterwards?

I think the proper fix is to *not* decrease the active_connections
in case of connection failure[1], i.e. when state ==
CONN_QUIT_SENT.

However, I do not really understand the _s != _p_s->count
condition in MYSQLND_DEC_STATISTIC[2] and MYSQLND_INC_STATISTIC.
_s is an enum value; why would it match a count?

[1] <https://github.com/php/php-src/blob/php-7.4.22/ext/mysqlnd/mysqlnd_connection.c#L1235>
[2] <https://github.com/php/php-src/blob/php-7.4.22/ext/mysqlnd/mysqlnd_statistics.h#L58>
 
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