netdev - Re: [PATCH net-next 3/4] tls: kernel TLS support

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Date:   Fri, 26 May 2017 08:49:52 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     davejwatson@...com, ilyal@...lanox.com, aviadye@...lanox.com,
        borisp@...lanox.com, liranl@...lanox.com, matanb@...lanox.com,
        netdev@...r.kernel.org, tom@...bertland.com,
        herbert@...dor.apana.org.au, linux-crypto@...r.kernel.org,
        hannes@...essinduktion.org, alexei.starovoitov@...il.com,
        nmav@...lts.org, fridolin.pokorny@...il.com
Subject: Re: [PATCH net-next 3/4] tls: kernel TLS support

On Fri, 2017-05-26 at 11:18 -0400, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Fri, 26 May 2017 07:16:59 -0700
> 
> > On Wed, 2017-05-24 at 09:27 -0700, Dave Watson wrote:
> >> Software implementation of transport layer security, implemented using ULP
> >> infrastructure.  tcp proto_ops are replaced with tls equivalents of sendmsg and
> >> sendpage.
> > 
> > ...
> > 
> >> +
> >> +int tls_sw_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
> >> +{
> > 	...
> >> +
> >> +	lock_sock(sk);
> >> +
> >> +	/* Only one writer at a time is allowed */
> >> +	if (sk->sk_write_pending)
> >> +		return -EBUSY;
> > 
> > Ouch...
> 
> Well, as I understand it, it is the same restriction userspace must
> itself enforce either in the application or in the SSL library.

The problem here is to lock_sock(sk), then returning without releasing
the socket.

Some basic lock imbalance really.