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

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Message-ID: <20171222073606.GC27149@gondor.apana.org.au>
Date:   Fri, 22 Dec 2017 18:36:07 +1100
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Stephan Müller <smueller@...onox.de>
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

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.

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.

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt