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[2012-01-10 16:43 UTC] daan at react dot com
Description: ------------ A simple object construction where a __toString() stores $this, will trigger a segfault during garbage collection at the end of the request. Probably related bug: https://bugs.php.net/bug.php?id=60598 Is a distilled version of this bug: https://bugs.php.net/bug.php?id=60457 Test script: --------------- <?php class Container { public function getObject() { $this->object = new StringableObject(); return $this->object; } // This destructor is required to exist to trigger the segfault public function __destruct() { } } class StringableObject { public function __toString() { $this->test = $this; return ''; } } $container = new Container(); $object = $container->getObject(); // Any kind of function which triggers a 'to string' object conversion // Casting $object with (string) will circumvent the problem echo trim($object); // Another call is required to corrupt heap echo trim('test'); Expected result: ---------------- test Actual result: -------------- Segfault gdb backtrace (with commandline PHP with build tag ZEND_DEBUG_OBJECTS) [Thread debugging using libthread_db enabled] Allocated object id #1 Allocated object id #2 Increased refcount of object id #2 Decreased refcount of object id #2 testIncreased refcount of object id #1 Decreased refcount of object id #1 Deallocated object id #1 Program received signal SIGSEGV, Segmentation fault. 0x00000000006d4c69 in gc_zval_possible_root (zv=0x1023e40) at /home/sjon/php- debug/php-5.3.8/Zend/zend_gc.c:143 143 GC_ZOBJ_CHECK_POSSIBLE_ROOT(zv); (gdb) bt #0 0x00000000006d4c69 in gc_zval_possible_root (zv=0x1023e40) at /home/sjon/php-debug/php-5.3.8/Zend/zend_gc.c:143 #1 0x00000000006c4ad8 in zend_hash_destroy (ht=0x10266d0) at /home/sjon/php- debug/php-5.3.8/Zend/zend_hash.c:529 #2 0x00000000006d6009 in zend_object_std_dtor (object=0x1023dc8) at /home/sjon/php-debug/php-5.3.8/Zend/zend_objects.c:45 #3 0x00000000006d6029 in zend_objects_free_object_storage (object=0x1023dc8) at /home/sjon/php-debug/php-5.3.8/Zend/zend_objects.c:126 #4 0x00000000006da037 in zend_objects_store_del_ref_by_handle_ex (handle=2, handlers=<optimized out>) at /home/sjon/php-debug/php- 5.3.8/Zend/zend_objects_API.c:220 #5 0x00000000006da053 in zend_objects_store_del_ref (zobject=0x1022350) at /home/sjon/php-debug/php-5.3.8/Zend/zend_objects_API.c:172 #6 0x00000000006a9571 in _zval_dtor (zvalue=0x1022350) at /home/sjon/php- debug/php-5.3.8/Zend/zend_variables.h:35 #7 _zval_ptr_dtor (zval_ptr=<optimized out>) at /home/sjon/php-debug/php- 5.3.8/Zend/zend_execute_API.c:447 #8 0x00000000006c3645 in zend_hash_apply_deleter (ht=0xe33188, p=0x1026728) at /home/sjon/php-debug/php-5.3.8/Zend/zend_hash.c:612 #9 0x00000000006c4f81 in zend_hash_reverse_apply (ht=0xe33188, apply_func=0x6a9430 <zval_call_destructor>) at /home/sjon/php-debug/php- 5.3.8/Zend/zend_hash.c:762 #10 0x00000000006a9921 in shutdown_destructors () at /home/sjon/php-debug/php- 5.3.8/Zend/zend_execute_API.c:226 #11 0x00000000006b7747 in zend_call_destructors () at /home/sjon/php-debug/php- 5.3.8/Zend/zend.c:875 #12 0x00000000006651fd in php_request_shutdown (dummy=<optimized out>) at /home/sjon/php-debug/php-5.3.8/main/main.c:1594 #13 0x000000000042d105 in main (argc=2, argv=0x7fffffffebb8) at /home/sjon/php- debug/php-5.3.8/sapi/cli/php_cli.c:1363 (gdb) frame 2 #2 0x00000000006d6009 in zend_object_std_dtor (object=0x1023dc8) at /home/sjon/php-debug/php-5.3.8/Zend/zend_objects.c:45 45 zend_hash_destroy(object->properties); (gdb) print object->ce->name $1 = 0x1025af0 "StringableObject" (gdb) frame 1 #1 0x00000000006c4ad8 in zend_hash_destroy (ht=0x10266d0) at /home/sjon/php- debug/php-5.3.8/Zend/zend_hash.c:529 529 ht->pDestructor(q->pData); (gdb) print_ht ht [0x010266d0] { "test\0" => [0x01023e40] (refcount=-1) object Program received signal SIGSEGV, Segmentation fault. 0x00000000006da0a4 in zend_object_store_get_object (zobject=0x1023e40) at /home/sjon/php-debug/php-5.3.8/Zend/zend_objects_API.c:272 272 return EG(objects_store).object_buckets[handle].bucket.obj.object; The program being debugged was signaled while in a function called from GDB. GDB remains in the frame where the signal was received. To change this behavior use "set unwindonsignal on". Evaluation of the expression containing the function (zend_objects_get_address) will be abandoned. When the function is done executing, GDB will silently stop. (gdb) Patchesbug60701.patch (last revision 2012-01-20 13:30 UTC by hans at rakers dot org)Pull RequestsHistoryAllCommentsChangesGit/SVN commits
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I'm not sure I understand the patch, especially this part: if (readobj == writeobj) { + if (Z_REFCOUNT_P(readobj) <= 1) { + INIT_PZVAL(writeobj); + } zval_dtor(readobj); It looks like you initializing the object and then immediately calling dtor on it (since readobj == writeobj). Could you explain why and what you are trying to do there?5.3.10 fixed the attached testcase, a more simple test now fails. <?php class A { public $a; public function __toString() { $this->a = $this; return 'waa?'; } } $a = new A; echo trim($a); echo trim($a->a); Results: 5.3.0 - 5.3.9 waa?1 5.3.10 waa? Warning: trim() expects parameter 1 to be string, unknown given in /home/deployer/public_html/php/tmp/ba8096acaf18c52bc12e38619634c25b on line 14 5.4.0 Segmentationfault