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PharFileInfo just takes a pointer from the manifest without refcounting anything. If the entry is then removed from the manifest while the PharFileInfo object still exists, we get a UAF. We fix this by using the fp_refcount field. This is technically a behaviour change as the unlinking is now blocked, and potentially file modifications can be blocked as well. The alternative would be to have a field that indicates whether deletion is blocked, but similar corruption bugs may occur as well with file overwrites, so we increment fp_refcount instead. This also fixes an issue where a destructor called multiple times resulted in a UAF as well, by moving the NULL'ing of the entry field out of the if.
devnexen
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Feb 15, 2025
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LGTM, IMHO fp_refcount handling should have its macros on master. I do not know if there any gain you can get changing all these bitfields in phar_entry_info.
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PharFileInfo just takes a pointer from the manifest without refcounting anything. If the entry is then removed from the manifest while the PharFileInfo object still exists, we get a UAF.
We fix this by using the fp_refcount field. This is technically a behaviour change as the unlinking is now blocked, and potentially file modifications can be blocked as well. The alternative would be to have a field that indicates whether deletion is blocked, but similar corruption bugs may occur as well with file overwrites, so we increment fp_refcount instead.
This also fixes an issue where a destructor called multiple times resulted in a UAF as well, by moving the NULL'ing of the entry field out of the if.