netdev - Re: [PATCH net-next 1/5] tcp: Create list of TFO-contexts

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Date:   Mon, 17 Dec 2018 07:49:58 -0800
From:   Christoph Paasch <cpaasch@...le.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH net-next 1/5] tcp: Create list of TFO-contexts

On 16/12/18 - 22:31:41, Eric Dumazet wrote:
> 
> 
> On 12/14/2018 02:40 PM, Christoph Paasch wrote:
> > Instead of having a single TFO-context, we now have a list of
> > tcp_fastopen_context, bounded by TCP_FASTOPEN_CTXT_LEN (set to 2).
> > 
> > This enables us to do a rolling TFO-key update that allows the server to
> > accept old cookies and at the same time announce new ones to the client
> > (see follow-up patch).
> > 
> > Signed-off-by: Christoph Paasch <cpaasch@...le.com>
> > ---
> >  include/net/tcp.h       |  2 ++
> >  net/ipv4/tcp_fastopen.c | 52 +++++++++++++++++++++++++++++++++++++++++++++----
> >  2 files changed, 50 insertions(+), 4 deletions(-)
> > 
> > diff --git a/include/net/tcp.h b/include/net/tcp.h
> > index e0a65c067662..e629ea2e6c9d 100644
> > --- a/include/net/tcp.h
> > +++ b/include/net/tcp.h
> > @@ -1622,9 +1622,11 @@ bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
> >  			     struct tcp_fastopen_cookie *cookie);
> >  bool tcp_fastopen_defer_connect(struct sock *sk, int *err);
> >  #define TCP_FASTOPEN_KEY_LENGTH 16
> > +#define TCP_FASTOPEN_CTXT_LEN 2
> >  
> >  /* Fastopen key context */
> >  struct tcp_fastopen_context {
> > +	struct tcp_fastopen_context __rcu *next;
> >  	struct crypto_cipher	*tfm;
> >  	__u8			key[TCP_FASTOPEN_KEY_LENGTH];
> >  	struct rcu_head		rcu;
> > diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
> > index 018a48477355..c52d5b8eabf0 100644
> > --- a/net/ipv4/tcp_fastopen.c
> > +++ b/net/ipv4/tcp_fastopen.c
> > @@ -37,8 +37,14 @@ static void tcp_fastopen_ctx_free(struct rcu_head *head)
> >  {
> >  	struct tcp_fastopen_context *ctx =
> >  	    container_of(head, struct tcp_fastopen_context, rcu);
> > -	crypto_free_cipher(ctx->tfm);
> > -	kfree(ctx);
> > +
> > +	while (ctx) {
> > +		struct tcp_fastopen_context *prev = ctx;
> > +		/* We own ctx, thus no need to hold the Fastopen-lock */
> > +		ctx = rcu_dereference_protected(ctx->next, 1);
> > +		crypto_free_cipher(prev->tfm);
> > +		kfree(prev);
> > +	}
> >
> 
> It seems this function does not need to be changed, since at most one context
> should be freed per run ?

It gets called from tcp_fastopen_destroy_cipher() though (to destroy the
socket's TFO-keys when the socket gets closed). There it has to destroy the
whole list.

Same when going through exit_batch for the namespace.


We could of course split it in tcp_fastopen_ctx_free_one() and
tcp_fastopen_ctx_free_all(). But maybe that's overkill as it's a rare thing
to do?


Christoph