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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1b2c5c1b-0089-5790-6c3a-ff86645a5ec0@canonical.com>
Date:   Wed, 11 Apr 2018 15:17:59 +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 15:10, David Howells wrote:
> Colin Ian King <colin.king@...onical.com> wrote:
> 
>>>> -	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.
> 
> It would be possible to cast the value to u64 before assigning it, I suppose.
> Would that help?  E.g.:
> 
> 	mask = (u64)((1 << nr_slots) - 1);
> 
> It looks a bit odd, though, since the cast is made implicitly anyway.

I'm not sure that actually helps,  1 << nr_slots is still evaluating as
a 32 bit value, so that final cast does not may any difference.  Anyhow,
since nr_slots is less than 32 then keeping it the way it was is fine.

> 
> David
> --
> To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in
> the body of a message to majordomo@...r.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>