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

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Message-ID: <1499283.NSekfIF0FQ@tauon.atsec.com>
Date:	Thu, 09 Jun 2016 20:24:17 +0200
From:	Stephan Mueller <smueller@...onox.de>
To:	Mat Martineau <mathew.j.martineau@...ux.intel.com>
Cc:	Tadeusz Struk <tadeusz.struk@...el.com>, 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

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?

Ciao
Stephan