In the Linux kernel, the following vulnerability has been resolved:
ALSA: scarlett2: Use a private URB for the notification endpoint
scarlett2_init_notify() used mixer->urb, which
snd_usb_mixer_status_create() allocates for the UAC2 status interrupt
endpoint and mixer.c manages. On a device with that endpoint, the
“already in use” check fires on the status URB and returns 0 for
success without doing anything. No notification URB is submitted, and
cmd_done is left zeroed because it is initialised past that check and
nowhere else. scarlett2_usb_init() then issues SCARLETT2_USB_INIT_1
and wait_for_completion_timeout() would crash adding to the zeroed
wait.head.
Use a separate URB in scarlett2_data, as done for FCP, and initialise
cmd_done in scarlett2_init_private(). mixer.c was also freeing the URB
in snd_usb_mixer_free() and resubmitting it in
snd_usb_mixer_activate(), so scarlett2 must now do both: add
scarlett2_cleanup_urb(), called from private_free and private_suspend,
and a private_resume callback to re-establish the URB after resume.
scarlett2_init_notify() is reached from there, and the URB kill path
in scarlett2_notify() completes cmd_done, leaving a stale count that
would satisfy the next command’s wait before the device ACKs. Use
reinit_completion() to clear it.
Also free the URB if the transfer buffer allocation fails, and both if
usb_submit_urb() fails. Move scarlett2_init_notify() up next to
scarlett2_cleanup_urb() so scarlett2_init_private() can reference it
without a forward declaration.
