Re: [PATCH] ALSA: usx2y: Initialize idle URBs before submitting streams

[Takashi Iwai]

On Wed, 28 Oct 2026 11:31:58 +0100,
YuanZhe Liu wrote:
> 
> usb_stream_start() submits the first two capture and playback URBs and
> only afterwards assigns sk->idle_inurb, sk->idle_outurb,
> sk->completed_inurb and sk->completed_outurb to the remaining two URBs
> of each direction.
> 
> A transfer can complete as soon as usb_submit_urb() has been called, so
> the completion handler i_capture_start() or i_playback_start() may run
> before those pointers are set.  While the stream is still being
> synchronized (state below usb_stream_sync1), stream_start() then calls
> playback_prep_freqn(sk, sk->idle_outurb) with sk->idle_outurb still
> NULL, and the packet descriptors are written through that NULL pointer:
> 
>   Oops: general protection fault, probably for non-canonical address
>   0xdffffc0000000018: 0000 [#1] SMP KASAN
>   KASAN: null-ptr-deref in range [0x00000000000000c0-0x00000000000000c7]
>   RIP: 0010:playback_prep_freqn+0x11c/0x4a0 sound/usb/usx2y/usb_stream.c:33
>   Call Trace:
>    <IRQ>
>    stream_start+0x5dc/0x8d0 sound/usb/usx2y/usb_stream.c:596
>    i_capture_start+0x3da/0x710 sound/usb/usx2y/usb_stream.c:654
>    __usb_hcd_giveback_urb+0x238/0x550 drivers/usb/core/hcd.c:1657
>    usb_giveback_urb_bh+0x20b/0x530 drivers/usb/core/hcd.c:1691
>    tasklet_hi_action+0xa/0x20 kernel/softirq.c:994
>    handle_softirqs+0x16f/0x440 kernel/softirq.c:645
>    </IRQ>
> 
> The four URBs referenced by these pointers are allocated long before and
> do not depend on any transfer state, so assign them before the submit
> loop.  Keeping the assignment inside the retry path also restores a
> well-defined URB rotation when the start frame mismatch handling kills
> and resubmits the streams.
> 
> Fixes: 030a07e441296c372f946cd4065b5d831d8dc40c ("ALSA: Add USB US122L driver")
> Cc: stable@xxxxxxxxxxxxxxx
> Co-developed-by: Bin Yu <byu@xxxxxxxxxxxxx>
> Signed-off-by: Bin Yu <byu@xxxxxxxxxxxxx>
> Co-developed-by: Cheng Wen <wencheng@xxxxxxxxxxxxx>
> Signed-off-by: Cheng Wen <wencheng@xxxxxxxxxxxxx>
> Signed-off-by: YuanZhe Liu <25031212351@xxxxxxxxxxxxxxxxx>

Applied now.  Thanks.


Takashi