Edit report at http://bugs.php.net/bug.php?id=53306&edit=1
ID: 53306
User updated by: mike at harschsystems dot com
Reported by: mike at harschsystems dot com
Summary: php crashes with segfault when DTrace
"exception-thrown" probe fires
Status: Assigned
Type: Bug
Package: Reproducible crash
Operating System: Mac OS X and Solaris
PHP Version: trunk-SVN-2010-11-13 (snap)
Assigned To: dsp
Block user comment: N
New Comment:
With the patch in place, I can use the following DTrace script to see
exceptions
getting thrown and caught (differentiating those with null input from
those with
valid pointers):
#!/usr/sbin/dtrace -s
#pragma D option quiet
php*:::exception-thrown
/arg0 == NULL/
{
printf("PHP Exception Thrown. Classname: Unknown\n");
}
php*:::exception-thrown
/arg0 != NULL/
{
printf("PHP Exception Thrown. ");
printf("Classname: %s\n", copyinstr(arg0));
}
php*:::exception-caught
{
printf("PHP Exception Caught. ");
printf("Classname: %s\n", copyinstr(arg0));
}
Running this script with the trivial exception script mentioned in this
bug,
produces the following output:
# ./php_exception.d
PHP Exception Thrown. Classname: Exception
PHP Exception Thrown. Classname: Unknown
PHP Exception Caught. Classname: Exception
^C
So, we see that 2 exceptions are being thrown (one with a valid pointer
and one
with a null pointer), and one exception is caught.
Previous Comments:
------------------------------------------------------------------------
[2010-11-13 23:25:12] mike at harschsystems dot com
sorry, just uploaded patch file "exception_fix2.patch"
------------------------------------------------------------------------
[2010-11-13 23:19:49] [email protected]
Where is the patch?
------------------------------------------------------------------------
[2010-11-13 23:12:55] mike at harschsystems dot com
Description:
------------
When DTrace is present, and a DTrace consumer has enabled the
"php*:::exception-
thrown" probe, php will crash when the probe fires, due to a null
reference passed
to zend_get_object_classname() from within the probe context. The code
within the
DTrace probe context (inside zend_throw_exception_internal() ) doesn't
check that
the 'exception' argument is non-NULL. The test described here obviously
creates
an instance where 'exception' is NULL, and when the enabled probe fires
- the
enabled code calls zend_get_object_classname() with a null argument,
resulting in
the segfault.
Test script:
---------------
In order to reproduce this, you must be running on a system that
supports DTrace (OS X, Solaris, FreeBSD?), and php must have been built
with --enable-dtrace.
The following script will trigger the exception codepath we're
interested in:
<html><head><title>Test for PHP Exceptions</title></head><body>
<?php
function my_func($my_arg) {
if ($my_arg == 0)
throw new Exception('You cannot do that.');
}
try {
echo '<p>attempting to call my_func with my_arg == 0';
my_func(0);
echo 'this will not be executed';
} catch (Exception $e) {
echo "<p>caught exception: " . $e->getMessage();
}
?>
</body></html>
This will run fine when DTrace hasn't enabled the exception-thrown
probe, but if we run the following command (as root) at the time that
the above script is requested, php will crash.
# dtrace -n 'php*:::exception-thrown {}'
The attached patch shows how the problem could be avoided - though I'd
like to hear from someone familiar with the Zend framework - to see if
there may be an upstream bug that's causing the NULL value to come into
zend_throw_exception_internal() in the first place. If this is expected
behavior, we should anticipate it and provide appropriate handling
within the DTrace probe.
Expected result:
----------------
PHP shouldn't crash.
Actual result:
--------------
PHP crashes as shown:
Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x0000000000000008
0x000000010156818b in zend_get_object_classname (object=0x0,
class_name=0x7fff5fbfeb60,
class_name_len=0x7fff5fbfeb6c) at
/Users/michaelharsch/Desktop/php-trunk-
201011131530/Zend/zend_API.c:253
253 if (Z_OBJ_HT_P(object)->get_class_name == NULL ||
(gdb) bt
#0 0x000000010156818b in zend_get_object_classname (object=0x0,
class_name=0x7fff5fbfeb60,
class_name_len=0x7fff5fbfeb6c) at
/Users/michaelharsch/Desktop/php-trunk-
201011131530/Zend/zend_API.c:253
#1 0x0000000101589e2e in zend_throw_exception_internal (exception=0x0)
at
/Users/michaelharsch/Desktop/php-trunk-
201011131530/Zend/zend_exceptions.c:90
#2 0x00000001015a6543 in zend_do_fcall_common_helper_SPEC
(execute_data=0x10051a0d8) at zend_vm_execute.h:735
#3 0x00000001015acc98 in ZEND_DO_FCALL_SPEC_CONST_HANDLER
(execute_data=0x10051a0d8) at zend_vm_execute.h:2015
#4 0x00000001015a4075 in execute (op_array=0x10054f030) at
zend_vm_execute.h:410
#5 0x000000010154e6e5 in dtrace_execute (op_array=0x10054f030) at
/Users/michaelharsch/Desktop/php-trunk-
201011131530/Zend/zend_dtrace.c:75
#6 0x00000001015674c6 in zend_execute_scripts (type=8, retval=0x0,
file_count=3) at
/Users/michaelharsch/Desktop/php-trunk-201011131530/Zend/zend.c:1195
#7 0x00000001014d28e3 in php_execute_script
(primary_file=0x7fff5fbff810) at
/Users/michaelharsch/Desktop/php-trunk-
201011131530/main/main.c:2340
#8 0x00000001016a39c5 in php_handler (r=0x10098a2a8) at
/Users/michaelharsch/Desktop/php-trunk-
201011131530/sapi/apache2handler/sapi_apache2.c:667
#9 0x00000001000021db in ap_run_handler ()
#10 0x0000000100002aba in ap_invoke_handler ()
#11 0x000000010002f738 in ap_process_request ()
#12 0x000000010002bfa9 in ap_process_http_connection ()
#13 0x0000000100013737 in ap_run_process_connection ()
#14 0x0000000100013bd1 in ap_process_connection ()
#15 0x00000001000363f2 in child_main ()
#16 0x00000001000364dc in make_child ()
#17 0x0000000100036aaf in ap_mpm_run ()
#18 0x000000010000a821 in main ()
------------------------------------------------------------------------
--
Edit this bug report at http://bugs.php.net/bug.php?id=53306&edit=1
