ALSA: firewire-lib: Avoid division by zero in apply_constraint_to_size()

The step variable is initialized to zero. It is changed in the loop,
but if it's not changed it will remain zero. Add a variable check
before the division.

The observed behavior was introduced by commit 826b5de
("ALSA: firewire-lib: fix insufficient PCM rule for period/buffer size"),
and it is difficult to show that any of the interval parameters will
satisfy the snd_interval_test() condition with data from the
amdtp_rate_table[] table.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 826b5de ("ALSA: firewire-lib: fix insufficient PCM rule for period/buffer size")
Signed-off-by: Andrey Shumilin <[email protected]>
Reviewed-by: Takashi Sakamoto <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Takashi Iwai <[email protected]>

Author: Andrey Shumilin

sound/firewire/amdtp-stream.c

@@ -172,6 +172,9 @@ static int apply_constraint_to_size(struct snd_pcm_hw_params *params,
 			step = max(step, amdtp_syt_intervals[i]);
 	}
 
+	if (step == 0)
+		return -EINVAL;
+
 	t.min = roundup(s->min, step);
 	t.max = rounddown(s->max, step);
 	t.integer = 1;