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Date:   Tue, 12 Jan 2021 14:58:35 +0100
Message-ID: <s5hturmqmt0.wl-tiwai@suse.de>
From:   Takashi Iwai <tiwai@suse.de>
To:     Geert Uytterhoeven <geert+renesas@glider.be>
Cc:     Clemens Ladisch <clemens@ladisch.de>,
        Takashi Sakamoto <o-takashi@sakamocchi.jp>,
        Jaroslav Kysela <perex@perex.cz>,
        Takashi Iwai <tiwai@suse.com>, alsa-devel@alsa-project.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH/RFC 1/2] ALSA: fireface: Fix integer overflow in transmit_midi_msg()
In-Reply-To: <20210111130251.361335-2-geert+renesas@glider.be>
References: <20210111130251.361335-1-geert+renesas@glider.be>
        <20210111130251.361335-2-geert+renesas@glider.be>
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On Mon, 11 Jan 2021 14:02:50 +0100,
Geert Uytterhoeven wrote:
> 
> 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")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.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