linux-kernel - Re: [PATCH v6 3/6] crypto: AF_ALG -- add asymmetric cipher interface

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Date:	Fri, 10 Jun 2016 07:42:00 -0700
From:	Tadeusz Struk <tadeusz.struk@...el.com>
To:	Stephan Mueller <smueller@...onox.de>,
	Mat Martineau <mathew.j.martineau@...ux.intel.com>
Cc:	dhowells@...hat.com, herbert@...dor.apana.org.au,
	linux-api@...r.kernel.org, marcel@...tmann.org,
	linux-kernel@...r.kernel.org, keyrings@...r.kernel.org,
	linux-crypto@...r.kernel.org, dwmw2@...radead.org,
	davem@...emloft.net
Subject: Re: [PATCH v6 3/6] crypto: AF_ALG -- add asymmetric cipher interface

On 06/09/2016 11:36 AM, Stephan Mueller wrote:
> Am Donnerstag, 9. Juni 2016, 11:27:13 schrieb Mat Martineau:
> 
> Hi Mat, Tadeusz,
> 
>> On Thu, 9 Jun 2016, Stephan Mueller wrote:
>>> Am Donnerstag, 9. Juni 2016, 11:18:04 schrieb Mat Martineau:
>>>
>>> Hi Mat,
>>>
>>>>> Or is your concern that the user space interface restricts things too
>>>>> much
>>>>> and thus prevents a valid use case?
>>>>
>>>> The latter - my primary concern is the constraint this places on
>>>> userspace
>>>> by forcing larger buffer sizes than might be necessary for the operation.
>>>> struct akcipher_request has separate members for src_len and dst_len, and
>>>> dst_len is documented as needing "to be at least as big as the expected
>>>> result depending on the operation". Not the maximum result, the expected
>>>> result. It's also documented that the cipher will generate an error if
>>>> dst_len is insufficient and update the value with the required size.
>>>>
>>>> I'm updating some userspace TLS code that worked with an earlier,
>>>> unmerged
>>>> patch set for AF_ALG akcipher (from last year). The read calls with
>>>> shorter buffers were the main porting problem.
>>>
>>> I see -- are you proposing to drop that check entirely?
>>
>> Yes.
> 
> Ok, after checking the code again, I think that dropping that sanity check 
> should be ok given that this length is part of the akcipher API.
> 
> Tadeusz, as you are currently managing that patch set, would you re-spin it 
> with the following check removed?
> 
> +     if (usedpages < akcipher_calcsize(ctx)) {
> +             err = -EMSGSIZE;
> +             goto unlock;
> +     }
> 

Ok, I'll update the patch.
Thanks,
-- 
TS