Edit report at http://bugs.php.net/bug.php?id=40846&edit=1
ID: 40846 Comment by: wclark at xoom dot org Reported by: crisp at xs4all dot nl Summary: pcre.backtrack_limit too restrictive Status: Open Type: Feature/Change Request Package: Feature/Change Request Operating System: all PHP Version: 5.2.1 New Comment: Please just set the PHP limits to match the default PCRE limits. People asked for that three years ago.. what's the holdup? I run into this problem quite regularly when using UNGREEDY matches, which frankly makes no sense (why would UN-greedy matches need more backtracking?) but I'll chalk that up to PCRE's poor implementation. Regardless, if the PHP defaults were set higher I would never encounter these issues in the first place. Previous Comments: ------------------------------------------------------------------------ [2009-08-28 08:54:44] tom at r dot je This is still an issue in 5.3. The low limit causes scripts which hit it to fail without a warning, notice or error, creating hard to track down bugs For example, something which works fine for one set of data stops working on another set because the data is just longer. This cannot be the expected behaviour, surely? At minimum there needs to be a warning. Ideally though, the limit needs to be put to the pcre defaults. ------------------------------------------------------------------------ [2007-12-10 14:18:11] daan at react dot nl This issue is still a problem, plus this low setting is also the cause of segfaults. (see http://bugs.php.net/bug.php?id=43031) At the moment even this simple regexp segfaults 5.2.5: preg_match('/(.)*/', str_repeat('x', 6000)); I hope that is not intended behavior, as is suggested in the reply in bug report 43031. ------------------------------------------------------------------------ [2007-08-16 19:00:13] drnick at physics dot byu dot edu I just wanted to throw out that I completely agree with crisp. We recently updated PHP on our webserver to 5.2.3 and had issues with our template system on input sizes of a certain size (>100K). The idea of allowing PHP to enforce limits on the PCRE library is fine, but having the default action (when recursion_limit and backtrack_limit are commented-out) be PHP overriding PCRE's internal limits is VERY problematic. Aside from being incredibly anti backwards-compatible, I believe PHP should not make arbitrary assumptions such as these. I believe PHP should be changed so that the default action is to make use of PCRE's internal limits, and if people want to enforce their own, they can make that decision via the options. Perhaps modify php.ini-recommended to explain the options and say why having external limits can be good. ------------------------------------------------------------------------ [2007-08-16 15:58:08] brandon at invisionpower dot com Installations of 5.2 are causing this issue for us with relatively simple regex. Users can submit an arbitrary amount of data (I work on a bulletin board software) that is parsed out for bbcode tags. Even simple expressions are causing problems. $txt = preg_replace_callback( "#\[code\](.+?)\[/code\]#is", array( &$this, 'regex_code_tag' ), $txt ); var_dump( preg_last_error() ); The callback function is not being hit at all and the output is int(2) (backtrack limit hit). Increasing backtrack limit to 1,000,000 "resolves" the issue, but with shared hosting plans it's unrealistic to expect hosts to make php.ini changes to allow this. I agree with crisp - the limit in PHP should bet set to the internal PCRE options, with the php.ini settings allowing you to reduce them if you wish. PHP should not arbitrarily reduce them. ------------------------------------------------------------------------ [2007-05-20 11:22:00] crisp at xs4all dot nl PHP 5.2.0 includes an update of the PCRE library (version 6.7), so some problems may not be totally due to the restrictive limits of the PCRE settings in PHP but could be a bug/regression in PCRE itself. PCRE has always been very poor in internal optimisation of expressions that contain look-aheads or look-behinds, especially when they are combined with some OR'ed subexpression. It's backtracking mechanism is quite simplistic and doesn't rule out execution paths that are sure not to result in a match - in fact, it doesn't have any sort of execution planner. ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at http://bugs.php.net/bug.php?id=40846 -- Edit this bug report at http://bugs.php.net/bug.php?id=40846&edit=1
