AZL-96105

In the Linux kernel, the following vulnerability has been resolved:

ALSA: usb-audio: fix use-after-free in umptoendpoint()

createmidi2ump() registers a card-owned sndumpendpoint and stores a back-pointer to its per-interface sndusbmidi2ump object in ump->privatedata, but it never installs an ump->private_free hook and never clears that pointer.

If a later step of sndusbmidiv2create() fails, its error path calls freeallmidi2umps(), which kfree()s the sndusbmidi2ump object while the already-registered endpoint keeps pointing at it. The created /dev/snd/umpCD node stays exposed, so the first operation of any UMP open, umptoendpoint(), dereferences the dangling ump->private_data and reads rmidi->eps[dir] out of freed memory.

A malicious USB MIDI 2.0 device that makes creation fail after the endpoint is registered can thus trigger a slab use-after-free read on a subsequent open of the UMP node.

Clear the endpoint's back-pointer before freeing the object, and let umptoendpoint() tolerate a NULL private_data so the open/close/trigger callbacks fail cleanly (their callers already handle a NULL endpoint) instead of dereferencing a stale pointer.

Discovered by XBOW, triaged by Baul Lee baul.lee@xbow.com