vmwgfx Driver File Descriptor Handling Privilege Escalation

If the vmwgfx driver fails to copy the fence_rep object to userland, it tries to recover by deallocating the (already populated) file descriptor. This is wrong, as the fd gets released via put_unused_fd() which shouldn't be used, as the fd table slot was already populated via the previous call to fd_install(). This leaves userland with a valid fd table entry pointing to a freed file object. The authors use this bug to overwrite a SUID binary with their payload and …

authors bug call copy driver entry escalation file handling object privilege privilege escalation recover userland valid