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streams: Fix UAF when a user wrapper unregisters itself - #24754
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Prior to the new stream APIs it would've been easy to hold onto uwrap->ce and then we didn't need all this refcount juggling.
It's still possible to do this and then use php_stream_wrapper_warn_name...
What do you think?
A user wrapper's constructor, destructor or __set() can unregister the wrapper while unlink(), rename(), mkdir(), rmdir(), touch(), chmod() or stat() is using it, which frees the wrapper, and the code then reads the freed wrapper to find the class constructor and to build the "is not implemented!" warning. Read the class entry before any user code runs, pass it to user_stream_create_object(), and report the warning by the user-space wrapper name.
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Agreed, reworked that way. |
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Thanks.
I like this approach better for two reasons:
- It's simpler
- No refcount juggling
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A user stream wrapper whose constructor, destructor or __set() calls stream_wrapper_unregister() frees the wrapper while unlink(), rename(), mkdir(), rmdir(), touch(), chmod() or stat() is still using it; the constructor lookup and the "is not implemented!" warning then read the freed wrapper. These operations now read the class entry before any user code runs, user_stream_create_object() takes the class entry instead of the wrapper, and the warning is reported through php_stream_wrapper_warn_name(). Found while reviewing #24711, which fixes failed opendir() handling on PHP-8.6.