linux-kernel - Re: dm-crypt accepts '+' in the key

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Message-ID: <20161114003631.GA1304@avx2>
Date:   Mon, 14 Nov 2016 03:36:32 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Milan Broz <gmazyland@...il.com>
Cc:     Mikulas Patocka <mpatocka@...hat.com>,
        Ondrej Kozina <okozina@...hat.com>,
        Mike Snitzer <msnitzer@...hat.com>, dm-devel@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: dm-crypt accepts '+' in the key

On Sun, Nov 13, 2016 at 03:45:27PM +0100, Milan Broz wrote:
> On 11/12/2016 09:20 PM, Mikulas Patocka wrote:
> > Hi
> > 
> > dm-crypt uses the function kstrtou8 to decode the encryption key. kstrtou8 
> > calls kstrtoull and kstrtoull skips the first character if it is '+'.
> > 
> > Consequently, it is possible to load keys with '+' in it. For example, 
> > this is possible:
> > 
> > dmsetup create cr --table "0 131072 crypt aes-cbc-essiv:sha256 +0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0 0 /dev/debian/tmptest 0"
> > 
> > Should this be fixed in dm-crypt or in kstrtou8? A fix in kstrtou8 could 
> > be more appropriate, but we don't know how many other kernel parts depend 
> > on this "skip plus" behavior...
> 
> I would way it should be checked in both places...
> For dmcrypt, it should validate input here and should
> not accept anything in key field in dm table that is not in hexa representation.
> 
> (Is this regression since code switched from simple_strtoul to  kstrtou8
> or this bug was there always?)

Well, before kernel would silently parse anything broken as "0".

But since it is base-16, "0[xX]" will be accepted before every byte.

dm-crypt should parse key by hand, frankly.