ALSA: usb-audio: fix OOB write in snd_usbmidi_akai_output()

Browse source

commit 0970274613 upstream.

snd_usbmidi_akai_output() computes its fill-loop bound

	buf_end = ep->max_transfer - MAX_AKAI_SYSEX_LEN - 1;

as a signed int, so a small device-advertised bulk-OUT max_transfer
makes buf_end negative.  The loop guard then compares the u32
urb->transfer_buffer_length against that negative int: the usual
arithmetic conversion turns buf_end into a large unsigned value, so the
guard stays true and each iteration keeps appending SysEx framing and
payload bytes past the end of the URB transfer buffer, which is only
max_transfer bytes long.

A USB device that advertises a tiny bulk-OUT endpoint can therefore
trigger an attacker-length- and content-controlled heap out-of-bounds
write when a process writes to the created /dev/snd/midiC*D* node.

Return early when there is no room for even one SysEx, so the loop is
never entered with a bound that would wrap.  The loop is the last
statement of the function, so bailing out is equivalent to it not
running.

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

Fixes: 4434ade8c9 ("ALSA: usb-audio: add support for Akai MPD16")
Suggested-by: Takashi Iwai <tiwai@suse.de>
Reported-by: Federico Kirschbaum <federico.kirschbaum@xbow.com>
Reported-by: Baul Lee <baul.lee@xbow.com>
Cc: stable@vger.kernel.org
Signed-off-by: Baul Lee <baul.lee@xbow.com>
Link: https://patch.msgid.link/20260726074500.50145-1-baul.lee@xbow.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

...

This commit is contained in:

Baul Lee 2026-07-26 16:45:00 +09:00 • committed by Greg Kroah-Hartman

parent 4f762bfc53

commit 00cc659a42

1 changed files with 2 additions and 0 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

2

sound/usb/midi.c

View file