Bug #70232 [NEW]: Incorrect bump-along behavior with \K and empty string match

From: nhahtdh at gmail dot com Operating system: PHP version: 5.6.12 Package: PCRE related Bug Type: Bug Bug description:Incorrect bump-along behavior with \K and empty string match Description: ------------ Please see the test case, the expected result and the actual result in the bug report below. From analyzing the code, I have identified that the error comes from the following line of code (plus similar code in other functions): https://github.com/php/php-src/blob/0787cd60ed3d0c8c8c8ff7e49b9bb3587bf33b64/ext/pcre/php_pcre.c#L891 g_notempty = (offsets[1] == offsets[0])? PCRE_NOTEMPTY | PCRE_ANCHORED : 0; /* Advance to the position right after the last full match */ start_offset = offsets[1]; This part of the code checks whether the match is empty. If the match it empty, it tries to perform another match from the last position of the match with PCRE_NOTEMPTY flag to force the match to be non-empty. However, it's incorrect to set the PCRE_NOTEMPTY flag by checking the length of the match based on the start and end indices of the match. For the regex in the test case ~(?: |\G)\d\B\K~ (which always results in empty string matches due to \K), the index where we execute the match from (start_offset) and the start index of the match (offsets[0]) are always different. Therefore, the regex actually advances ahead in the string, and setting PCRE_NOTEMPTY in such case rejects valid empty string matches. I believe (offsets[1] == offsets[0]) should be changed to (offsets[1] == start_offset). If start_offset <= offsets[0] <= offsets[1] is an invariant, then the change should be correct. Original report and analysis: http://chat.stackoverflow.com/transcript/message/24995536#24995536 Test script: --------------- <? $str = "123 a123 1234567 b123 123"; $str = preg_replace('~(?: |\G)\d\B\K~', "*", $str); echo $str; ?> Expected result: ---------------- 1*2*3 a123 1*2*3*4*5*6*7 b123 1*2*3 The expected result (10 matches/replacements) can be observed on - pcretest with PCRE version 8.35 2014-04-04 - regex101 https://regex101.com/r/oP9mZ7/3 Actual result: -------------- 1*23 a123 1*23*45*67 b123 1*23 -- Edit bug report at https://bugs.php.net/bug.php?id=70232&edit=1 -- Try a snapshot (PHP 5.4): https://bugs.php.net/fix.php?id=70232&r=trysnapshot54 Try a snapshot (PHP 5.5): https://bugs.php.net/fix.php?id=70232&r=trysnapshot55 Try a snapshot (trunk): https://bugs.php.net/fix.php?id=70232&r=trysnapshottrunk Fixed in SVN: https://bugs.php.net/fix.php?id=70232&r=fixed Fixed in release: https://bugs.php.net/fix.php?id=70232&r=alreadyfixed Need backtrace: https://bugs.php.net/fix.php?id=70232&r=needtrace Need Reproduce Script: https://bugs.php.net/fix.php?id=70232&r=needscript Try newer version: https://bugs.php.net/fix.php?id=70232&r=oldversion Not developer issue: https://bugs.php.net/fix.php?id=70232&r=support Expected behavior: https://bugs.php.net/fix.php?id=70232&r=notwrong Not enough info: https://bugs.php.net/fix.php?id=70232&r=notenoughinfo Submitted twice: https://bugs.php.net/fix.php?id=70232&r=submittedtwice register_globals: https://bugs.php.net/fix.php?id=70232&r=globals PHP 4 support discontinued: https://bugs.php.net/fix.php?id=70232&r=php4 Daylight Savings: https://bugs.php.net/fix.php?id=70232&r=dst IIS Stability: https://bugs.php.net/fix.php?id=70232&r=isapi Install GNU Sed: https://bugs.php.net/fix.php?id=70232&r=gnused Floating point limitations: https://bugs.php.net/fix.php?id=70232&r=float No Zend Extensions: https://bugs.php.net/fix.php?id=70232&r=nozend MySQL Configuration Error: https://bugs.php.net/fix.php?id=70232&r=mysqlcfg