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

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Message-ID: <3079.1567173701@warthog.procyon.org.uk>
Date:   Fri, 30 Aug 2019 15:01:41 +0100
From:   David Howells <dhowells@...hat.com>
To:     Colin King <colin.king@...onical.com>
Cc:     dhowells@...hat.com, 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

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.

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

David