On Fri, May 03, 2024 at 01:28:37PM -0700, Kees Cook wrote: > > Is this the right approach? It still feels to me like get_file() needs > to happen much earlier... I don't believe it needs to happen at all. The problem is not that ->release() can be called during ->poll() - it can't and it doesn't. It's that this instance of ->poll() is trying to extend the lifetime of that struct file, when it might very well be past the point of no return. What we need is * promise that ep_item_poll() won't happen after eventpoll_release_file(). AFAICS, we do have that. * ->poll() not playing silly buggers. As it is, dma_buf ->poll() is very suspicious regardless of that mess - it can grab reference to file for unspecified interval. Have that happen shortly before reboot and you are asking for failing umount. ->poll() must be refcount-neutral wrt file passed to it. I'm seriously tempted to make ->poll() take const struct file * and see if there's anything else that would fall out.
