linux-kernel - Re: [PATCH][next] afs: fix integer overflow when shifting 1 more than 32 places

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Message-ID: <62e9abc2-b639-419c-afa7-e89054f7dce9@canonical.com>
Date:   Wed, 11 Apr 2018 14:42:47 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-afs@...ts.infradead.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] afs: fix integer overflow when shifting 1 more than
 32 places

On 11/04/18 14:39, David Howells wrote:
> Colin King <colin.king@...onical.com> wrote:
> 
>> Shifting 1 (a 32 bit signed int) more than 32 places will overflow
>> the int, so explicitly use 1ULL to avoid this overflow.
>> ...
>> -	mask = (1 << nr_slots) - 1;
>> +	mask = (1ULL << nr_slots) - 1;
> 
> nr_slots cannot be larger than 9, so what I wrote is actually fine and is more
> efficient on a 32-bit machine.

ok, sorry about the noise.

> 
> David
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