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From: Dan Carpenter <dan.carpenter@oracle.com>
To: David Howells <dhowells@redhat.com>
Cc: Colin Ian King <colin.king@canonical.com>,
	linux-afs@lists.infradead.org, kernel-janitors@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH][next] afs: fix integer overflow when shifting 1 more than 32 places
Date: Wed, 11 Apr 2018 18:58:12 +0300	[thread overview]
Message-ID: <20180411155811.2qznymjhi6zlzgbb@mwanda> (raw)
In-Reply-To: <24493.1523455816@warthog.procyon.org.uk>

On Wed, Apr 11, 2018 at 03:10:16PM +0100, David Howells wrote:
> Colin Ian King <colin.king@canonical.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.

My feeling is that makes it worse.  It would introduce a secret,
unpublished static checker warning on my build and it doesn't help me as
a reviewer.

Ideally static analyzers should know that nr_slots is 0-9, but right now
that seems pretty tricky to figure out...

regards,
dan carpenter

WARNING: multiple messages have this Message-ID (diff)
From: Dan Carpenter <dan.carpenter@oracle.com>
To: David Howells <dhowells@redhat.com>
Cc: Colin Ian King <colin.king@canonical.com>,
	linux-afs@lists.infradead.org, kernel-janitors@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH][next] afs: fix integer overflow when shifting 1 more than 32 places
Date: Wed, 11 Apr 2018 15:58:12 +0000	[thread overview]
Message-ID: <20180411155811.2qznymjhi6zlzgbb@mwanda> (raw)
In-Reply-To: <24493.1523455816@warthog.procyon.org.uk>

On Wed, Apr 11, 2018 at 03:10:16PM +0100, David Howells wrote:
> Colin Ian King <colin.king@canonical.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.

My feeling is that makes it worse.  It would introduce a secret,
unpublished static checker warning on my build and it doesn't help me as
a reviewer.

Ideally static analyzers should know that nr_slots is 0-9, but right now
that seems pretty tricky to figure out...

regards,
dan carpenter


  parent reply	other threads:[~2018-04-11 15:58 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-11 13:26 [PATCH][next] afs: fix integer overflow when shifting 1 more than 32 places Colin King
2018-04-11 13:26 ` Colin King
2018-04-11 13:39 ` David Howells
2018-04-11 13:39   ` David Howells
2018-04-11 13:42   ` Colin Ian King
2018-04-11 13:42     ` Colin Ian King
2018-04-11 14:10   ` David Howells
2018-04-11 14:10     ` David Howells
2018-04-11 14:17     ` Colin Ian King
2018-04-11 14:17       ` Colin Ian King
2018-04-11 15:58     ` Dan Carpenter [this message]
2018-04-11 15:58       ` Dan Carpenter
2018-04-11 16:03     ` David Howells
2018-04-11 16:03       ` David Howells

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