netdev - Re: [PATCH] ipv6: udp packets following an UFO enqueued packet need also be handled by UFO

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Date:	Mon, 30 Sep 2013 19:23:12 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Jiri Pirko <jiri@...nulli.us>
Cc:	netdev@...r.kernel.org, yoshfuji@...ux-ipv6.org,
	davem@...emloft.net
Subject: Re: [PATCH] ipv6: udp packets following an UFO enqueued packet need also be handled by UFO

On Mon, Sep 30, 2013 at 01:43:43PM +0200, Jiri Pirko wrote:
> Sat, Sep 21, 2013 at 06:27:00AM CEST, hannes@...essinduktion.org wrote:
> >In the following scenario the socket is corked:
> >If the first UDP packet is larger then the mtu we try to append it to the
> >write queue via ip6_ufo_append_data. A following packet, which is smaller
> >than the mtu would be appended to the already queued up gso-skb via
> >plain ip6_append_data. This causes random memory corruptions.
> >
> >In ip6_ufo_append_data we also have to be careful to not queue up the
> >same skb multiple times. So setup the gso frame only when no first skb
> >is available.
> >
> >This also fixes a shortcoming where we add the current packet's length to
> >cork->length but return early because of a packet > mtu with dontfrag set
> >(instead of sutracting it again).
> >
> >Found with trinity.
> >
> >Cc: YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
> >Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
> >---
> >
> >I could only test this with virtualized UFO enabled network cards. Could
> >someone test this on real hardware?
> >
> > net/ipv6/ip6_output.c | 53 +++++++++++++++++++++------------------------------
> > 1 file changed, 22 insertions(+), 31 deletions(-)
> >
> >diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> >index 3a692d5..a54c45c 100644
> >--- a/net/ipv6/ip6_output.c
> >+++ b/net/ipv6/ip6_output.c
> >@@ -1015,6 +1015,8 @@ static inline int ip6_ufo_append_data(struct sock *sk,
> > 	 * udp datagram
> > 	 */
> > 	if ((skb = skb_peek_tail(&sk->sk_write_queue)) == NULL) {
> >+		struct frag_hdr fhdr;
> >+
> > 		skb = sock_alloc_send_skb(sk,
> > 			hh_len + fragheaderlen + transhdrlen + 20,
> > 			(flags & MSG_DONTWAIT), &err);
> >@@ -1036,12 +1038,6 @@ static inline int ip6_ufo_append_data(struct sock *sk,
> > 		skb->protocol = htons(ETH_P_IPV6);
> > 		skb->ip_summed = CHECKSUM_PARTIAL;
> > 		skb->csum = 0;
> >-	}
> >-
> >-	err = skb_append_datato_frags(sk,skb, getfrag, from,
> >-				      (length - transhdrlen));
> >-	if (!err) {
> >-		struct frag_hdr fhdr;
> > 
> > 		/* Specify the length of each IPv6 datagram fragment.
> > 		 * It has to be a multiple of 8.
> >@@ -1052,15 +1048,10 @@ static inline int ip6_ufo_append_data(struct sock *sk,
> > 		ipv6_select_ident(&fhdr, rt);
> > 		skb_shinfo(skb)->ip6_frag_id = fhdr.identification;
> > 		__skb_queue_tail(&sk->sk_write_queue, skb);
> >-
> >-		return 0;
> > 	}
> >-	/* There is not enough support do UPD LSO,
> >-	 * so follow normal path
> >-	 */
> >-	kfree_skb(skb);
> > 
> >-	return err;
> >+	return skb_append_datato_frags(sk, skb, getfrag, from,
> >+				       (length - transhdrlen));
> > }
> > 
> 
> What if non-ufo-path-created skb is peeked?

You mean like:
first append a frame < mtu
second frame > mtu so it gets handles by ip6_ufo_append?

Currently I don't see a problem with it but I may be wrong. What is
your suspicion?

Greetings,

  Hannes

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