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Date: Mon, 12 May 2014 19:03:22 +0200
From: Jilles Tjoelker <jilles@stack.nl>
To: Andrey Chernov <ache@freebsd.org>
Subject: Re: svn commit: r265901 - stable/10/sys/kern
Message-ID: <20140512170322.GA2479@stack.nl>
References: <201405120427.s4C4RAZf093033@svn.freebsd.org>
 <5370F110.5050502@freebsd.org>
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Cc: svn-src-stable@freebsd.org, Don Lewis <truckman@FreeBSD.org>,
 src-committers@freebsd.org, svn-src-stable-10@freebsd.org,
 svn-src-all@freebsd.org
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On Mon, May 12, 2014 at 08:04:32PM +0400, Andrey Chernov wrote:
> On 12.05.2014 8:27, Don Lewis wrote:
> > +	if (start + amask < start) {
> > +		DPRINTF(("start+amask wrapped around\n"));
> > +		goto out;
> > +	}

> Checking for overflow _after_ it happens is unportable and dangerous,
> since wrapping around is not only one possible result. They should be
> rewritten like that:

> if (start > ULONG_MAX - amask)

Unsigned types wrap around per the C standard. Overflow checking after
it happens is fine.

You are right for signed types.

-- 
Jilles Tjoelker