ALSA: fireface: Fix integer overflow in transmit_midi_msg()

As snd_ff.rx_bytes[] is unsigned int, and NSEC_PER_SEC is 1000000000L,
the second multiplication in

    ff->rx_bytes[port] * 8 * NSEC_PER_SEC / 31250

always overflows on 32-bit platforms, truncating the result.  Fix this
by precalculating "NSEC_PER_SEC / 31250", which is an integer constant.

Note that this assumes ff->rx_bytes[port] <= 16777.

Fixes: 19174295788de77d ("ALSA: fireface: add transaction support")
Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20210111130251.361335-2-geert+renesas@glider.be
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/firewire/fireface/ff-transaction.c b/sound/firewire/fireface/ff-transaction.c
index 7f82762..ee7122c 100644 (file)
--- a/sound/firewire/fireface/ff-transaction.c
+++ b/sound/firewire/fireface/ff-transaction.c
@@ -88,7 +88,7 @@ static void transmit_midi_msg(struct snd_ff *ff, unsigned int port)
 
        /* Set interval to next transaction. */
        ff->next_ktime[port] = ktime_add_ns(ktime_get(),
-                               ff->rx_bytes[port] * 8 * NSEC_PER_SEC / 31250);
+                       ff->rx_bytes[port] * 8 * (NSEC_PER_SEC / 31250));
 
        if (quad_count == 1)
                tcode = TCODE_WRITE_QUADLET_REQUEST;