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Date: Tue, 29 Apr 2008 03:27:14 -0700 (PDT)
From: David Miller <davem@...emloft.net>
To: bkostya@...mail.com
Cc: netdev@...r.kernel.org, herbert@...dor.apana.org.au
Subject: Re: [PATCH][IPv4] UFO: prevent generation of chained skb
From: Kostya B <bkostya@...mail.com>
Date: Mon, 28 Apr 2008 12:13:27 +0000
>
> [IPv4] UFO: prevent generation of chained skb destined to UFO device
>
> Problem:
> ip_append_data() could wrongly generate a chained skb for devices which support UFO.
> When sk_write_queue is not empty (e.g. MSG_MORE), __instead__ of appending data
> into the next nr_frag of the queued skb, a new chained skb is created.
>
> I would normally assume UFO device should get data in nr_frags and not in frag_list.
> Later the udp4_hwcsum_outgoing() resets csum to NONE and skb_gso_segment() has oops.
>
> Proposal:
> 1. Even length is less than mtu, employ ip_ufo_append_data() and append data to the __existed__ skb in the sk_write_queue.
>
> 2. ip_ufo_append_data() is fixed due to a wrong manipulation of peek-ing and later enqueue-ing of the same skb.
> Now, enqueuing is always performed, because on error the further ip_flush_pending_frames() would release the queued skb.
>
>
> Signed-off-by: Kostya B
Mostly this looks fine to me.
Herbert, can you take a quick look at this?
Thanks.
>
> ---
>
> net/ipv4/ip_output.c | 25 +++++++++----------------
> 1 file changed, 9 insertions(+), 16 deletions(-)
>
> diff -uprN -X linux-2.6.25-git11/Documentation/dontdiff linux-2.6.25-git11/net/ipv4/ip_output.c linux-2.6.25-git11-fix/net/ipv4/ip_output.c
> --- linux-2.6.25-git11/net/ipv4/ip_output.c 2008-04-28 12:22:00.000000000 +0300
> +++ linux-2.6.25-git11-fix/net/ipv4/ip_output.c 2008-04-28 14:02:41.000000000 +0300
> @@ -753,23 +753,15 @@ static inline int ip_ufo_append_data(str
> skb->ip_summed = CHECKSUM_PARTIAL;
> skb->csum = 0;
> sk->sk_sndmsg_off = 0;
> +
> + /* specify the length of each IP datagram fragment*/
> + skb_shinfo(skb)->gso_size = mtu - fragheaderlen;
> + skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
> + __skb_queue_tail(&sk->sk_write_queue, skb);
> }
>
> - err = skb_append_datato_frags(sk,skb, getfrag, from,
> + return skb_append_datato_frags(sk,skb, getfrag, from,
> (length - transhdrlen));
> - if (!err) {
> - /* specify the length of each IP datagram fragment*/
> - skb_shinfo(skb)->gso_size = mtu - fragheaderlen;
> - skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
> - __skb_queue_tail(&sk->sk_write_queue, skb);
> -
> - return 0;
> - }
> - /* There is not enough support do UFO ,
> - * so follow normal path
> - */
> - kfree_skb(skb);
> - return err;
> }
>
> /*
> @@ -863,8 +855,9 @@ int ip_append_data(struct sock *sk,
> csummode = CHECKSUM_PARTIAL;
>
> inet->cork.length += length;
> - if (((length> mtu) && (sk->sk_protocol == IPPROTO_UDP)) &&
> - (rt->u.dst.dev->features & NETIF_F_UFO)) {
> + if (((length> mtu) || !skb_queue_empty(&sk->sk_write_queue)) &&
> + (sk->sk_protocol == IPPROTO_UDP) &&
> + (rt->u.dst.dev->features & NETIF_F_UFO)) {
>
> err = ip_ufo_append_data(sk, getfrag, from, length, hh_len,
> fragheaderlen, transhdrlen, mtu,
> ---
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