ALSA: usx2y: Require a buffer of two URBs

usx2y_urb_capt_retire() wraps the ring buffer once per packet and
usx2y_urb_play_prepare() once per URB of nr_of_packs() packets of up to
50 frames. Both assume that the data fits in the buffer, and the hw
constraints only require about two 1 ms periods, so a packet larger
than the buffer on capture, or a URB larger than the buffer on playback,
violates that assumption.

Constrain SNDRV_PCM_HW_PARAM_BUFFER_SIZE in snd_usx2y_pcm_open() to at
least two URBs, 2 * nr_of_packs() * 50 frames, for both directions. The
bound is in frames and derived from the driver's own packet limit, so it
does not read the endpoint, whose altsetting is only selected in
prepare. Two URBs rather than one, because the position advances by a
URB on playback and only moves when a URB is less than the whole buffer.
Keep a guard in usx2y_urb_capt_retire() that drops a packet larger than
the buffer, for the case the constraint makes unreachable.

With nrpacks above about 163 (S16_LE) or 109 (S24_3LE) the bound exceeds
the 64 KiB buffer the substream preallocates (twice that with the
preallocation raised to its 128 KiB maximum), so hw_params fails for
those module settings. That is intended: the driver cannot be safe with
a URB larger than half the largest buffer.

Reproduced on 7.3-rc7 with a USB/IP device presenting the US-122
interface layout and 1024-byte packets into a 512-byte capture 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

Tested on 7.3-rc7 with the same device, S16_LE at 44100 Hz, nrpacks 4,
so the bound is 400 frames. A 128-frame capture buffer and a 200-frame
playback buffer are refused at hw_params with EINVAL. A 400-frame buffer
streams for 30 s in each direction with the position advancing inside
the buffer and no KASAN report; the capture guard did not fire. The
same 400-frame capture buffer with S24_3LE, which selects altsetting 2
in prepare, streams for 30 s with the same result.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Sinan Turunc <enscrpt@pm.me>
Link: https://patch.msgid.link/20261104122136.1518-2-enscrpt@pm.me
Signed-off-by: Takashi Iwai <tiwai@suse.de>

0 files changed, 0 insertions, 0 deletions