Re: [PATCH v2] ALSA: usx2y: Reject buffers smaller than two packets

[Takashi Iwai <tiwai@suse.de>]

On Wed, 04 Nov 2026 08:19:50 +0100,
Takashi Iwai wrote:
> 
> On Tue, 03 Nov 2026 14:23:03 +0100,
> Sinan Turunc wrote:
> > 
> > usx2y_urb_capt_retire() splits the copy into the ALSA ring buffer once
> > at the buffer end and wraps hwptr_done once, which is only correct when
> > one packet holds at most buffer_size frames. The packet size is the
> > endpoint's maxpacksize from usb_maxpacket(), while the hw constraints
> > allow 64-byte periods with periods_min 2, so a packet can be larger than
> > the whole buffer.
> > 
> > The endpoint is known at probe time, so constrain
> > SNDRV_PCM_HW_PARAM_BUFFER_BYTES in snd_usx2y_pcm_open() to at least
> > twice the endpoint's packet size. Two packets, matching the line6 fix.
> > The bound makes the copy safe, but it does not make every larger buffer
> > progress: the position is reported once per URB of 4 packets, so a
> > buffer that divides one URB's data returns to the same position at every
> > callback. That was already the case before this patch and is not changed
> > here. Keep a guard in usx2y_urb_capt_retire() that drops an oversized
> > packet with a ratelimited error, for the case that should no longer be
> > reachable.
> > 
> > Reproduced on 7.3-rc7 with a USB/IP device presenting the US-122
> > interface layout and 1024-byte packets into a 512-byte buffer:
> > 
> >   BUG: KASAN: out-of-bounds in i_usx2y_urb_complete+0x1285/0x1ac0
> >   Read of size 18446744073709551104 at addr ffff88800e448800 by task vhci_rx/83
> > 
> > With this patch a 1024-byte buffer is refused at hw_params; a 2048-byte
> > buffer is accepted and safe but barely advances (hw_ptr 9216 after 30 s,
> > for the reason above); a 3072-byte buffer streams for 30 s with no
> > report and with the position moving inside the buffer.
> > 
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Sinan Turunc <enscrpt@pm.me>
> 
> Applied now.  thanks.

... and I noticed Sashiko warnings now, so dropped again from the
queue.  Could you verify whether those complaints are valid or not?


thanks,

Takashi