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Date: Fri, 17 Aug 2018 06:33:12 -0400
From: Jeffrey Walton <noloader@...il.com>
To: oss-security@...ts.openwall.com
Cc: Florian Weimer <fweimer@...hat.com>, Doran Moppert <dmoppert@...hat.com>, 
	Christophe Fergeau <cfergeau@...hat.com>
Subject: Re: spice CVE-2018-10873: post-auth crash or potential
 heap corruption when demarshalling

On Fri, Aug 17, 2018 at 5:43 AM, Frediano Ziglio <fziglio@...hat.com> wrote:
>> On 08/17/2018 02:51 AM, Doran Moppert wrote:
>> >      +        if (SPICE_UNLIKELY((start + 2) > message_end)) {
>> >      +            goto error;
>> >      +        }
>>
>> These checks are still technically invalid because start + 2 is not a
>> valid pointer if it points past the allocated object.
>>
> Technical but not real. Unless it wraps is correct...

I believe Florian is correct. I think the most freedom you are allowed
is to access one beyond the "end" of the array; otherwise it is
undefined behavior. The compiler is free to remove the code or dragons
can fly out your nose.

Jeff

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