Bug #50207 [Com]: segmentation fault when concatenating very large strings on 64bit linux

Edit report at https://bugs.php.net/bug.php?id=50207&edit=1 ID: 50207 Comment by: mmmshuddup at live dot com Reported by: matt at bitwarehouse dot com Summary: segmentation fault when concatenating very large strings on 64bit linux Status: Closed Type: Bug Package: Scripting Engine problem Operating System: CentOS 5 x64 PHP Version: 5.*, 6 Block user comment: N Private report: N New Comment: Note that this has occurred on various different *nix systems, most notably CentOS 7. Using either PHP 5.5.20 or 5.6.6. That leads me to believe that this is probably an inherent bug that never got resolved because it probably never got noticed. Sorry for the lack of more information on the seg fault, I am not an actual C dev for PHP and I didn't pull enough info off the server. Hope this helps, best of luck! Previous Comments: ------------------------------------------------------------------------ [2015-03-09 06:05:09] mmmshuddup at live dot com I have experienced something similar. $words = explode(' ', $text); if (count($words) > $count) { $text = (string) join(' ', array_slice($words, 0, $count)); if ($ellipses) { $text = trim($text) . '...'; } } Segmentation fault occurs when base64 encoded images are in the string! (e.g. <img src="data:image/png;base64,iVBORw0KGgoA...." />) Now, in this case I don't think it's the length of the string itself that is the problem, but rather the the length of that "word," which in the case of a larger image, is a very very long string of characters with no whitespace separation. ------------------------------------------------------------------------ [2009-11-19 14:04:43] iliaa@php.net This bug has been fixed in SVN. Snapshots of the sources are packaged every three hours; this change will be in the next snapshot. You can grab the snapshot at http://snaps.php.net/. Thank you for the report, and for helping us make PHP better. ------------------------------------------------------------------------ [2009-11-19 14:04:35] svn@php.net Automatic comment from SVN on behalf of iliaa Revision: http://svn.php.net/viewvc/?view=revision&revision=290995 Log: Fixed bug #50207 (segmentation fault when concatenating very large strings on 64bit linux). ------------------------------------------------------------------------ [2009-11-17 18:36:43] matt at bitwarehouse dot com Clarification. The reproduce code should be: <?php // run me with: php -d memory_limit=-1 $s = str_repeat('A', pow(2,31)); $s .= 'B'; // fails with segfault printf("strlen: %u last-char: %c", strlen($s), $s[pow(2,31)]); ?> ------------------------------------------------------------------------ [2009-11-17 18:27:41] matt at bitwarehouse dot com Description: ------------ When concatenating values to a string of length >= 2^31, a segmentation fault will occur in memcpy on 64 bit Linux. This appears to be caused by the signed int length of the string (overflowed to negative) being cast to unsigned long long when added to an 8 byte pointer in Zend/zend_operators.c:concat_function. This also occurs in PHP 5.3.0. In PHP 5.1.6, a fatal erealloc error would be issued when the variable hit (2^31)+1 (INT_MAX) to prevent overflow. This however is gone in PHP >5.2. It is also unclear if PHP and its string functions are supposed to support strings larger than 2GB. Reproduce code: --------------- <?php // run me with: php -d memory_limit=-1 $s = str_repeat('A', pow(2,31)); $s .= 'B'; // fails with segfault printf("strlen: %u last-char: %c", strlen($s), $s[pow(2,31)-1]); ?> Expected result: ---------------- Either: strlen: 2147483649 last-char: B -or- "FATAL: erealloc(): Unable to allocate XXX bytes" with the understanding that strings cannot contain more than 2^31 bytes Actual result: -------------- PHP 5.2.11 and 5.3.0 were compiled with no configure arguments, no patches, no extra extensions on 64bit CentOS 5. E.g. ./configure && make #presume a.php contains reproduce code % ./sapi/cli/php -d memory_limit=-1 a.php Segmentation fault Backtrace of segfault: Program received signal SIGSEGV, Segmentation fault. 0x0000003897a7bdc1 in memcpy () from /lib64/libc.so.6 (gdb) bt #0 0x0000003897a7bdc1 in memcpy () from /lib64/libc.so.6 #1 0x000000000060a520 in concat_function (result=<value optimized out>, op1=0x1c32ba60, op2=0x1c32c850) at /home/matt/tmp/php- 5.2.11/Zend/zend_operators.c:1208 #2 0x0000000000676623 in zend_binary_assign_op_helper_SPEC_CV_CONST (binary_op=0x60a3c0 <concat_function>, execute_data=0x7fff4e789070) at /home/matt/tmp/php-5.2.11/Zend/zend_vm_execute.h:21034 #3 0x000000000062fd73 in execute (op_array=0x1c32c278) at /home/matt/tmp/php-5.2.11/Zend/zend_vm_execute.h:92 #4 0x00000000006117a3 in zend_execute_scripts (type=8, retval=0x2b47b33ea030, file_count=3) at /home/matt/tmp/php- 5.2.11/Zend/zend.c:1134 #5 0x00000000005d164b in php_execute_script (primary_file=0x7fff4e78b6e0) at /home/matt/tmp/php- 5.2.11/main/main.c:2020 #6 0x000000000069100c in main (argc=4, argv=0x7fff4e78b8d8) at /home/matt/tmp/php-5.2.11/sapi/cli/php_cli.c:1162 ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=50207&edit=1