linux-kernel - Re: [PATCH 2/3] crypto: ccp - return an actual key size from RSA max

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Message-ID: <087e7b27-f839-8d4b-8da8-5d0fa2f8caf1@maciej.szmigiero.name>
Date:   Sat, 3 Mar 2018 00:15:20 +0100
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     "David S. Miller" <davem@...emloft.net>,
        David Howells <dhowells@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Gary Hook <gary.hook@....com>, keyrings@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] crypto: ccp - return an actual key size from RSA
 max_size callback

On 02.03.2018 17:44, Herbert Xu wrote:
> On Sat, Feb 24, 2018 at 05:03:21PM +0100, Maciej S. Szmigiero wrote:
>> rsa-pkcs1pad uses a value returned from a RSA implementation max_size
>> callback as a size of an input buffer passed to the RSA implementation for
>> encrypt and sign operations.
>>
>> CCP RSA implementation uses a hardware input buffer which size depends only
>> on the current RSA key length, so it should return this key length in
>> the max_size callback, too.
>> This also matches what the kernel software RSA implementation does.
>>
>> Previously, the value returned from this callback was always the maximum
>> RSA key size the CCP hardware supports.
>> This resulted in this huge buffer being passed by rsa-pkcs1pad to CCP even
>> for smaller key sizes and then in a buffer overflow when ccp_run_rsa_cmd()
>> tried to copy this large input buffer into a RSA key length-sized hardware
>> input buffer.
>>
>> Signed-off-by: Maciej S. Szmigiero <mail@...iej.szmigiero.name>
>> Fixes: ceeec0afd684 ("crypto: ccp - Add support for RSA on the CCP")
>> Cc: stable@...r.kernel.org
> 
> Patch applied.  Thanks.

Thanks.

However, what about the first patch from this series?
Without it, while it no longer should cause a buffer overflow, in-kernel
X.509 certificate verification will still fail with CCP driver loaded
(since CCP RSA implementation has a higher priority than the software
RSA implementation).

Maciej