On Sat, 06 Feb 2021 08:48:05 +0100, Takashi Iwai wrote: > > On Sat, 06 Feb 2021 06:45:32 +0100, > Hillf Danton wrote: > > > > Due to the reconnecting key word mentioned, no fix to > > d0f09d1e4a88 ("ALSA: usb-audio: Refactoring endpoint URB deactivation") > > will be added. > > > > What is added is to capture EP_FLAG_STOPPING and remove the one > > second wait limit if the reconnecting acts may make it easier to > > repro the uaf. The diff is only for idea show. > > If my understanding is right, this won't change. The problem is > rather the lack of this function call itself, i.e. the missing > synchronization for the stream stop. > > It worked casually in the past because the endpoint resource is > released at a later point that is after all streams are really closed. > Now it's released earlier and hitting the UAF. ... and reading the code in a closer look, my guess was also wrong. The sync should have happened in snd_usb_endpoint_release(), and this didn't change for quite some time. So my previous fix won't be effective, too, I'm afraid. (And Hilif's patch won't help, either; if it's effective, there must have been a timeout error in the original case.) That said, I don't think this is a newly introduced regression, and race the condition could be in a hairy detail. Mikhail, can you reproduce this bug reliably? Takashi