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|ID||Project||Category||View Status||Date Submitted||Last Update|
|0001407||Xdebug||Stacktraces||public||2017-03-14 09:13||2017-04-14 12:59|
|Target Version||Fixed in Version|
|Summary||0001407: Not checking for NULL causes segfault|
|Description||(Marking this bug as private, feel free to make it public if you think this is not a serious thing).|
Hi, we have an in house developed PHP extension that I can probably not share publicly, so I will try to guide you through the problem as I see it.
|Steps To Reproduce||We are throwing an exception of our own exception class (also implemented in PHP's C bindings) using zend_throw_exception_ex().|
We end up in zend_exception_error() which somehow does not recognize the file property of our exception (perhaps exceptions that we write ourselves typically do not include a file property? I would be interested to know).
As you can see in , Zend expects the error callback to accept NULL for the filename, but Xdebug's xdebug_error_cb() always assume that it is safe to strdup() the filename  and segfaults when it reaches this state. The output of GDB's "bt is here:
(gdb) run lala.php
Starting program: /usr/bin/php lala.php
warning: no loadable sections found in added symbol-file system-supplied DSO at 0x7ffff7ffa000
[Thread debugging using libthread_db enabled]
Program received signal SIGSEGV, Segmentation fault.
__strlen_sse2 () at ../sysdeps/x86_64/strlen.S:32
32 movdqu (%rdi), %xmm1
Missing separate debuginfos, use: debuginfo-install libedit-2.11-4.20080712cvs.1.el6.x86_64 libidn-1.18-2.el6.x86_64 libtidy-0.99.0-19.20070615.1.el6.x86_64 lua-5.1.4-4.1.el6.x86_64
#0 __strlen_sse2 () at ../sysdeps/x86_64/strlen.S:32
#1 0x00007ffff51f3016 in __strdup (s=0x0) at strdup.c:42
0000002 0x00007ffff408154b in xdebug_error_cb (type=1, error_filename=0x0, error_lineno=0, format=0x67888c "Uncaught %s\n thrown", args=0x7fffffffbd20) at /usr/src/debug/php-pecl-xdebug-2.1.4/xdebug-2.1.4/xdebug_stack.c:496
0000003 0x00000000005bf8d3 in zend_error_va (type=<value optimized out>, file=<value optimized out>, lineno=<value optimized out>, format=<value optimized out>) at /usr/src/debug/php-5.3.3/Zend/zend_exceptions.c:752
0000004 0x00000000005bfa68 in zend_exception_error (exception=0xc72f50, severity=1) at /usr/src/debug/php-5.3.3/Zend/zend_exceptions.c:792
0000005 0x00000000005a81a2 in zend_execute_scripts (type=8, retval=0x0, file_count=3) at /usr/src/debug/php-5.3.3/Zend/zend.c:1259
0000006 0x0000000000555fb8 in php_execute_script (primary_file=0x7fffffffe500) at /usr/src/debug/php-5.3.3/main/main.c:2268
0000007 0x00000000006324c5 in main (argc=2, argv=0x7fffffffe708) at /usr/src/debug/php-5.3.3/sapi/cli/php_cli.c:1192
1: https://github.com/php/php-src/blob/c6982995504b6e21e8a5ade29cfb16a55196dc43/Zend/zend_exceptions.c#L1014 [^] (URL is for PHP's current master version, so this is still relevant)
2: https://github.com/xdebug/xdebug/blob/126514cf121ce3ecf6f92d26c1f661cb06e53406/xdebug_stack.c#L644 [^] (URL is for Xdebug's current master version, so this is still relevant)
|Additional Information||Old versions, I know :( They are/were receiving security patches from Red Hat at least, but I think the bug still exists in the current version of Xdebug.|
I am no C programmer so feel free to comment on what I did wrong or what else you would like to see. I am leaving this job in the beginning of April though, so feel free to contact me earlier than that if you need more information :)
|Tags||No tags attached.|
|Operating System||CentOS 6|
|Can you please share your lala.php script - I need a reproducible case before I can verify and fix it (and add a test case).|
The lala.php script is really simple and is no good for a minimally reproducible test case sadly (it constructs an object and calls a method that throws an exception, because the constructor did not receive good enough arguments).
Sadly I am not able to share the full code since it is not open source. In order to create a minimal reproducible case, I would need a couple of hours and I don't have that the next few days. I will try to come back to this in the end of this week.
If you want to try something out yourself, you could try to create a PHP module that includes a zend_class_entry that is an exception, and throw that exception from within the PHP module with zend_throw_exception().
Hi again Derick,
Too many other things needed getting done at work this week. I'll try to set some time off next week.
Have a nice weekend!
All right, I didn't get any time allocated to do this and I don't have access to this triggering code any longer. I'll share this ticket ID with my team but I'm unsure if they are interested in creating a PoC.
Sadly, my best tip until then, is to read the code and try to follow the variable-that-can-be-NULL-but-is-unaccounted-for backwards to the call site.
I have had another look, and the assumption that the error_file is not NULL is not in just one place. As I can't really see *how* this can be NULL, I am going to mark this bug as suspended, until there is a proof of concept.
thanks for the report!
|2017-03-14 09:13||chelmertz||New Issue|
|2017-03-14 11:19||derick||Note Added: 0004233|
|2017-03-14 11:19||derick||Assigned To||=> derick|
|2017-03-14 11:19||derick||Status||new => feedback|
|2017-03-14 11:19||derick||View Status||private => public|
|2017-03-14 12:44||chelmertz||Note Added: 0004234|
|2017-03-14 12:44||chelmertz||Status||feedback => assigned|
|2017-03-17 14:58||chelmertz||Note Added: 0004235|
|2017-04-04 11:53||chelmertz||Note Added: 0004250|
|2017-04-14 12:59||derick||Note Added: 0004262|
|2017-04-14 12:59||derick||Status||assigned => resolved|
|2017-04-14 12:59||derick||Resolution||open => suspended|
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