netdev - Re: [RFC] tcp md5 use of alloc

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Message-ID: <20141024093315.GA18290@gondor.apana.org.au>
Date:	Fri, 24 Oct 2014 17:33:15 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Crestez Dan Leonard <cdleonard@...il.com>
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org,
	linux-crypto@...r.kernel.org
Subject: Re: [RFC] tcp md5 use of alloc_percpu

Crestez Dan Leonard <cdleonard@...il.com> wrote:
>
>> Yep, but the sg stuff does not allow for stack variables. Because of
>> possible offloading and DMA, I dont know...
> A stack buffer is used in tcp_md5_hash_header to add a tcphdr to the 
> hash. A quick grep for sg_init_one find a couple of additional instances 
> of what looks like doing crypto on small stack buffers:

First of all crypto_hash_update is obsolete, don't use it in any
new code.  Thanks for reminding me to get rid of existing users.

You should either use crypto_shash_update for small data, e.g., headers
or crypto_ahash_update for large data such as whole packets.

If you use shash then you may allocate your buffer on the stack.  With
ahash stack memory is not allowed.

I hope this clears things up for you.

Cheers,
-- 
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
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