linux-kernel - Re: [PATCH] afs: use BIT_ULL for shifting to fix integer overflow

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Message-ID: <0a5df84f-920f-d2aa-69d6-963b40142f1f@canonical.com>
Date:   Fri, 30 Aug 2019 15:06:52 +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] afs: use BIT_ULL for shifting to fix integer overflow

On 30/08/2019 15:01, David Howells wrote:
> Colin King <colin.king@...onical.com> wrote:
> 
>> The expression 1 << nr_slots is evaluated with 32 bit integer arithmetic
>> and can overflow before it is widened.
> 
> If it does, it's an error on the part of the caller.  See the banner comment:
> 1 <= nr_slots <= 9.

Doh, totally missed that. My bad.

> 
> And, in any case, if nr_slots >= 64, using BIT_ULL wouldn't help...
> 
> David
>