Bug #77061 [NEW]: file_exists() race condition when used with symlinks

From: brandon dot jansen63 at gmail dot com Operating system: Windows 7/10 PHP version: 5.6.38 Package: *Directory/Filesystem functions Bug Type: Bug Bug description:file_exists() race condition when used with symlinks Description: ------------ If the following conditions are met: 1) Two simultaneous calls to file_exists() are made for the same file for which file_exists() would normally return TRUE, 2) The path given to file_exists() includes a directory which is a symlink (created with mklink /D), 3) PHP has not cached the real path of the file, Then one of the calls to file_exists() may return FALSE while the other returns TRUE. Test script: --------------- <?php echo "Starting...\r\n"; while( file_exists( 'C:\test_symlink\test.txt' ) ) { clearstatcache( true ); } echo "You shouldn't see this message.\r\n"; ?> Expected result: ---------------- Assuming that a file "test.txt" has been created somewhere on the file system, and that the symlink C:\test_symlink has been created with the following command: mklink /D C:\test_symlink <path-to-test.txt-containing-folder> Then when two instances of the test script are run in parallel, each should display the message "Starting..." and continue to run with no further output until manually terminated. Actual result: -------------- Each of the two instances of the test script displays "Starting...". However, after the second instance is started, one of the instances terminates with the message "You shouldn't see this message." -- Edit bug report at https://bugs.php.net/bug.php?id=77061&edit=1 -- Try a snapshot (PHP 5.4): https://bugs.php.net/fix.php?id=77061&r=trysnapshot54 Try a snapshot (PHP 5.5): https://bugs.php.net/fix.php?id=77061&r=trysnapshot55 Try a snapshot (trunk): https://bugs.php.net/fix.php?id=77061&r=trysnapshottrunk Fixed in SVN: https://bugs.php.net/fix.php?id=77061&r=fixed Fixed in release: https://bugs.php.net/fix.php?id=77061&r=alreadyfixed Need backtrace: https://bugs.php.net/fix.php?id=77061&r=needtrace Need Reproduce Script: https://bugs.php.net/fix.php?id=77061&r=needscript Try newer version: https://bugs.php.net/fix.php?id=77061&r=oldversion Not developer issue: https://bugs.php.net/fix.php?id=77061&r=support Expected behavior: https://bugs.php.net/fix.php?id=77061&r=notwrong Not enough info: https://bugs.php.net/fix.php?id=77061&r=notenoughinfo Submitted twice: https://bugs.php.net/fix.php?id=77061&r=submittedtwice register_globals: https://bugs.php.net/fix.php?id=77061&r=globals PHP 4 support discontinued: https://bugs.php.net/fix.php?id=77061&r=php4 Daylight Savings: https://bugs.php.net/fix.php?id=77061&r=dst IIS Stability: https://bugs.php.net/fix.php?id=77061&r=isapi Install GNU Sed: https://bugs.php.net/fix.php?id=77061&r=gnused Floating point limitations: https://bugs.php.net/fix.php?id=77061&r=float No Zend Extensions: https://bugs.php.net/fix.php?id=77061&r=nozend MySQL Configuration Error: https://bugs.php.net/fix.php?id=77061&r=mysqlcfg