linux-kernel - Re: [PATCH v2] crypto: AF_ALG

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Message-ID: <1779114.sJA4SrkMo1@tauon.chronox.de>
Date:   Fri, 22 Dec 2017 08:41:10 +0100
From:   Stephan Mueller <smueller@...onox.de>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     syzbot 
        <bot+b6e703f648ebbbf57a4528d4314e0c2a5c893dc2@...kaller.appspotmail.com>,
        davem@...emloft.net, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        ebiggers3@...il.com
Subject: Re: [PATCH v2] crypto: AF_ALG - limit mask and type

Am Freitag, 22. Dezember 2017, 08:36:07 CET schrieb Herbert Xu:

Hi Herbert,

> On Tue, Dec 19, 2017 at 07:25:04AM +0100, Stephan Müller wrote:
> > The user space interface allows specifying the type and the mask field
> > used to allocate the cipher. As user space can precisely select the
> > desired cipher by using either the name or the driver name, additional
> > selection options for cipher are not considered necessary and relevant
> > for user space.
> > 
> > This fixes a bug where user space is able to cause one cipher to be
> > registered multiple times potentially exhausting kernel memory.
> > 
> > Reported-by: syzbot <syzkaller@...glegroups.com>
> > Cc: <stable@...r.kernel.org>
> > Signed-off-by: Stephan Mueller <smueller@...onox.de>
> 
> This will break users of CRYPTO_ALG_KERN_DRIVER_ONLY.  I think
> we should add CRYPTO_ALG_TESTED to the blacklist since there is
> no sane reason to use it here.

Shouldn't we then rather use a white list instead of a black list?
> 
> Most other problems however would be bugs in the template code.
> The first thing a template does when it creates an instance is
> to check whether the resulting algorithm would fulfil the requested
> type/mask using crypto_check_attr_type.  So if that's not working
> then we should fix it there as it may also be triggered via other
> code paths that can create instances.

I think I understand that, but does user space need to utilize this logic?
> 
> Thanks,



Ciao
Stephan