netdev - Re: [PATCH v2 net-next] tcp: md5: use kmalloc() backed scratch areas

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Message-ID: <CALCETrUSi3T5JXMunEO9RM5ZEz=aA2xtf9encEVYGxJF4mbhKg@mail.gmail.com>
Date:	Mon, 27 Jun 2016 10:58:42 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 net-next] tcp: md5: use kmalloc() backed scratch areas

On Mon, Jun 27, 2016 at 9:51 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> From: Eric Dumazet <edumazet@...gle.com>
>
> Some arches have virtually mapped kernel stacks, or will soon have.
>
> tcp_md5_hash_header() uses an automatic variable to copy tcp header
> before mangling th->check and calling crypto function, which might
> be problematic on such arches.
>
> David says that using percpu storage is also problematic on non SMP
> builds.
>
> Just use kmalloc() to allocate scratch areas.

Seems reasonable.

I wonder if it's worth switching from ahash to shash, though.  It
would probably be simpler and faster.

--Andy