ALSA: pcm: oss: Limit the period size to 16MB

Set the practical limit to the period size (the fragment shift in OSS)
instead of a full 31bit; a too large value could lead to the exhaust
of memory as we allocate temporary buffers of the period size, too.

As of this patch, we set to 16MB limit, which should cover all use
cases.

Reported-by: syzbot+bb348e9f9a954d42746f@syzkaller.appspotmail.com
Reported-by: Bixuan Cui <cuibixuan@linux.alibaba.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/1638270978-42412-1-git-send-email-cuibixuan@linux.alibaba.com
Link: https://lore.kernel.org/r/20211201073606.11660-3-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/oss/pcm_oss.c

@@ -1962,7 +1962,7 @@ static int snd_pcm_oss_set_fragment1(struct snd_pcm_substream *substream, unsign
 	if (runtime->oss.subdivision || runtime->oss.fragshift)
 		return -EINVAL;
 	fragshift = val & 0xffff;
-	if (fragshift >= 31)
+	if (fragshift >= 25) /* should be large enough */
 		return -EINVAL;
 	runtime->oss.fragshift = fragshift;
 	runtime->oss.maxfrags = (val >> 16) & 0xffff;