linux-kernel - Re: [PATCH] mac80211: ethtool: avoid 32 bit multiplication overflow

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Message-ID: <1525784480.14830.12.camel@sipsolutions.net>
Date:   Tue, 08 May 2018 15:01:20 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Colin King <colin.king@...onical.com>,
        "David S . Miller" <davem@...emloft.net>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mac80211: ethtool: avoid 32 bit multiplication overflow

On Tue, 2018-05-08 at 13:57 +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> The multiplication of 100000 * cfg80211_calculate_bitrate() is a 32 bit
> operation and can overflow if cfg80211_calculate_bitrate is greater
> than 42949. Although I don't believe this is occurring at present, it
> would be safer to avoid the potential overflow by making the constant
> 100000 an ULL to ensure a 64 multiplication occurs.

Yeah it can't happen since mac80211 doesn't support 60 GHz devices, and
all others are limited to less than than.

Still, applied.

johannes