ALSA: firewire-tascam: Fix integer overflow in midi_port_work()

As snd_fw_async_midi_port.consume_bytes is unsigned int, and
NSEC_PER_SEC is 1000000000L, the second multiplication in

    port->consume_bytes * 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 port->consume_bytes <= 16777.

Fixes: 531f471834227d03 ("ALSA: firewire-lib/firewire-tascam: localize async midi port")
Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20210111130251.361335-3-geert+renesas@glider.be
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/firewire/tascam/tascam-transaction.c b/sound/firewire/tascam/tascam-transaction.c
index 90288b4b46379526527d953ee7a9ca9f2fe9eb3e..a073cece4a7d5e3aa2a45c1d5d148eb940cf67ae 100644 (file)
--- a/sound/firewire/tascam/tascam-transaction.c
+++ b/sound/firewire/tascam/tascam-transaction.c
@@ -209,7 +209,7 @@ static void midi_port_work(struct work_struct *work)
 
        /* Set interval to next transaction. */
        port->next_ktime = ktime_add_ns(ktime_get(),
-                               port->consume_bytes * 8 * NSEC_PER_SEC / 31250);
+                       port->consume_bytes * 8 * (NSEC_PER_SEC / 31250));
 
        /* Start this transaction. */
        port->idling = false;