Fix #79922: Crash after multiple calls to xml_parser_free() #5969
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We must not call `zend_list_delete()` in resource closer functions exposed to userland, because decreasing the refcount there leads to use-after-free scenarios. In this case, commit 4a42fbb worked for typical use-cases where `xml_parser_free()` has been called exactly once for the resource, because there is an internal zval (`->index`) referencing the same resource which already increased the refcount by one. However, when `xml_parser_free()` is called multiple times on the same XML parser resource, the resource would be freed prematurely. Instead we forcefully close the resource in `xml_parser_free()`. We also could decrease the refcount of the resource there, but that would require to call `xml_parser_free()` which is somewhat uncommon, and would be particularly bad wrt. PHP 8 where that function is a NOP, and as such doesn't have to be called. So we do no longer increase the refcount of the resource when copying it to the internal zval, and let the usualy refcounting semantics take care of the resource destruction. [1] <http://git.php.net/?p=php-src.git;a=commit;h=4a42fbbbc73aad7427aef5c89974d1833636e082>
nikic
approved these changes
Aug 10, 2020
|
Thanks! Applied as 0af3f49 (the AppVeyor failure is unrelated to this). |
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We must not call
zend_list_delete()in resource closer functionsexposed to userland, because decreasing the refcount there leads to
use-after-free scenarios. In this case, commit 4a42fbb worked for
typical use-cases where
xml_parser_free()has been called exactlyonce for the resource, because there is an internal zval (
->index)referencing the same resource which already increased the refcount by
one. However, when
xml_parser_free()is called multiple times on thesame XML parser resource, the resource would be freed prematurely.
Instead we forcefully close the resource in
xml_parser_free(). Wealso could decrease the refcount of the resource there, but that would
require to call
xml_parser_free()which is somewhat uncommon, andwould be particularly bad wrt. PHP 8 where that function is a NOP, and
as such doesn't have to be called. So we do no longer increase the
refcount of the resource when copying it to the internal zval, and let
the usualy refcounting semantics take care of the resource destruction.
[1] http://git.php.net/?p=php-src.git;a=commit;h=4a42fbbbc73aad7427aef5c89974d1833636e082