From: Baul Lee Date: Sun, 26 Jul 2026 05:13:37 +0000 (+0900) Subject: ALSA: usb-audio: fix use-after-free in ump_to_endpoint() X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4a05b2d1b4642df74f30b6f54843e825c4a2bfd3;p=thirdparty%2Flinux.git 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/umpC*D* 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 endpoint's 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 Fixes: ff49d1df79ae ("ALSA: usb-audio: USB MIDI 2.0 UMP support") Reported-by: Federico Kirschbaum Reported-by: Baul Lee Cc: stable@vger.kernel.org Signed-off-by: Baul Lee Link: https://patch.msgid.link/20260726051337.41124-1-baul.lee@xbow.com Signed-off-by: Takashi Iwai --- diff --git a/sound/usb/midi2.c b/sound/usb/midi2.c index 3ec633291772..83980fb83ac8 100644 --- a/sound/usb/midi2.c +++ b/sound/usb/midi2.c @@ -329,7 +329,7 @@ ump_to_endpoint(struct snd_ump_endpoint *ump, int dir) { struct snd_usb_midi2_ump *rmidi = ump->private_data; - return rmidi->eps[dir]; + return rmidi ? rmidi->eps[dir] : NULL; } /* ump open callback */ @@ -685,6 +685,8 @@ static void free_all_midi2_umps(struct snd_usb_midi2_interface *umidi) rmidi = list_first_entry(&umidi->rawmidi_list, struct snd_usb_midi2_ump, list); list_del(&rmidi->list); + if (rmidi->ump) + rmidi->ump->private_data = NULL; kfree(rmidi); } }