On Wed, Sep 25, 2024 at 07:52:37PM +0200, Alice Ryhl wrote: > > > I reviewed some other code paths to verify whether there are other > > > problems with processes dying concurrently with operations on freeze > > > notifications. I didn't notice any other memory safety issues, but I > > > > Yeah most other paths are protected with binder_procs_lock mutex. > > > > > noticed that binder_request_freeze_notification returns EINVAL if you > > > try to use it with a node from a dead process. That seems problematic, > > > as this means that there's no way to invoke that command without > > > risking an EINVAL error if the remote process dies. We should not > > > return EINVAL errors on correct usage of the driver. > > > > Agreed, this should probably be -ESRCH or something. I'll add it to v2, > > thanks for the suggestion. > > Well, maybe? I think it's best to not return errnos from these > commands at all, as they obscure how many commands were processed. This is problematic, particularly when it's a multi-command buffer. Userspace doesn't really know which one failed and if any of them succeeded. Agreed. > > Since the node still exists even if the process dies, perhaps we can > just let you create the freeze notification even if it's dead? We can > make it end up in the same state as if you request a freeze > notification and the process then dies afterwards. It's a dead node, there is no process associated with it. It would be incorrect to setup the notification as it doesn't have a frozen status anymore. We can't determine the ref->node->proc->is_frozen? We could silently fail and skip the notification, but I don't know if userspace will attempt to release it later... and fail with EINVAL. -- Carlos Llamas
