linux-kernel - Re: [PATCH/RFC 2/2] ALSA: firewire-tascam: Fix integer overflow in midi_port

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Date:   Tue, 12 Jan 2021 14:58:47 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Clemens Ladisch <clemens@...isch.de>,
        Takashi Sakamoto <o-takashi@...amocchi.jp>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH/RFC 2/2] ALSA: firewire-tascam: Fix integer overflow in midi_port_work()

On Mon, 11 Jan 2021 14:02:51 +0100,
Geert Uytterhoeven wrote:
> 
> 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")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> Compile-tested only.
> 
> I don't know the maximum transfer length of MIDI, but given it's an old
> standard, I guess it's rather small.  If it is larger than 16777, the
> constant "8" should be replaced by "8ULL", to force 64-bit arithmetic.

Applied now.  Thanks.


Takashi