In the Linux kernel, the following vulnerability has been resolved:
ALSA: usb-audio: fix use-after-free in ump_to_endpoint()
create_midi2_ump() registers a card-owned snd_ump_endpoint and stores a back-pointer to its per-interface snd_usb_midi2_ump object in ump->private_data, but it never installs an ump->private_free hook and never clears that pointer.
If a later step of snd_usb_midi_v2_create() fails, its error path calls free_all_midi2_umps(), which kfree()s the snd_usb_midi2_ump 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, ump_to_endpoint(), 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 endpoints back-pointer before freeing the object, and let ump_to_endpoint() 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
References
- https://git.kernel.org/stable/c/49eccef6d6e1c00dac6fb2e7eb6f9206c33e1c37
- https://git.kernel.org/stable/c/4a05b2d1b4642df74f30b6f54843e825c4a2bfd3
- https://git.kernel.org/stable/c/8a7a33b846d6ba695891b8d0040027cdbad8cd52
- https://git.kernel.org/stable/c/ae388c0e1bf727972096f770f82d12e4f748d1b6
- https://git.kernel.org/stable/c/cc014ebf803174f0e5d15956dfc5a38413c945ae