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Date: Fri, 11 Jul 2008 08:34:23 -0700
From: Stephen Hemminger <shemminger@...ux-foundation.org>
To: Simon Wunderlich <simon.wunderlich@...03.tu-chemnitz.de>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bridge: send correct MTU value in PMTU
On Fri, 11 Jul 2008 14:47:35 +0200
Simon Wunderlich <simon.wunderlich@...03.tu-chemnitz.de> wrote:
> When bridging interfaces with different MTUs, the bridge correctly
> chooses
> the minimum of the MTUs of the physical devices as the bridges MTU. But
> when a frame is passed which fits through the incoming, but not through
> the
> outgoing interface, a "Fragmentation Needed" packet is generated.
> However, the propagated MTU is hardcoded to 1500, which is wrong in this
> situation. The sender will repeat the packet again with the same frame
> size,
> and the same problem will occur again.
>
> Instead of sending 1500, the (correct) MTU value of the bridge is now
> sent via PMTU. To achieve this, the corresponding rtable structure is
> stored in its net_bridge structure.
>
> Signed-off-by: Simon Wunderlich <siwu@....tu-chemnitz.de>
> ---
> net/bridge/br_device.c | 5 ++++-
> net/bridge/br_if.c | 31 +++++++++++++++++++++++++++++++
> net/bridge/br_netfilter.c | 45 ++++++++++++---------------------------------
> net/bridge/br_private.h | 4 ++++
> 4 files changed, 51 insertions(+), 34 deletions(-)
>
> diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
> index bf77873..a52075b 100644
> --- a/net/bridge/br_device.c
> +++ b/net/bridge/br_device.c
> @@ -76,10 +76,13 @@ static int br_dev_stop(struct net_device *dev)
>
> static int br_change_mtu(struct net_device *dev, int new_mtu)
> {
> - if (new_mtu < 68 || new_mtu > br_min_mtu(netdev_priv(dev)))
> + struct net_bridge *br = netdev_priv(dev);
> + if (new_mtu < 68 || new_mtu > br_min_mtu(br))
> return -EINVAL;
>
> dev->mtu = new_mtu;
> + /* remember the MTU in the rtable for PMTU */
> + br->fake_rtable.u.dst.metrics[RTAX_MTU - 1] = new_mtu;
> return 0;
> }
>
> diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
> index f38cc53..b8d438d 100644
> --- a/net/bridge/br_if.c
> +++ b/net/bridge/br_if.c
> @@ -170,6 +170,34 @@ static void del_br(struct net_bridge *br)
> unregister_netdevice(br->dev);
> }
>
> +/* We need these fake structures to make netfilter happy --
> + * lots of places assume that skb->dst != NULL, which isn't
> + * all that unreasonable.
> + *
> + * Currently, we fill in the PMTU entry because netfilter
> + * refragmentation needs it, and the rt_flags entry because
> + * ipt_REJECT needs it. Future netfilter modules might
> + * require us to fill additional fields. */
> +struct net_device __fake_net_device = {
> + .hard_header_len = ETH_HLEN,
> +#ifdef CONFIG_NET_NS
> + .nd_net = &init_net,
> +#endif
> +};
> +
> +struct rtable __fake_rtable = {
> + .u = {
> + .dst = {
> + .__refcnt = ATOMIC_INIT(1),
> + .dev = &__fake_net_device,
> + .path = &__fake_rtable.u.dst,
> + .metrics = {[RTAX_MTU - 1] = 1500},
> + .flags = DST_NOXFRM,
> + }
> + },
> + .rt_flags = 0,
> +};
> +
> static struct net_device *new_bridge_dev(const char *name)
> {
> struct net_bridge *br;
> @@ -204,6 +232,9 @@ static struct net_device *new_bridge_dev(const char *name)
> br->topology_change = 0;
> br->topology_change_detected = 0;
> br->ageing_time = 300 * HZ;
> + memcpy(&br->fake_rtable, &__fake_rtable, sizeof(__fake_rtable));
> + br->fake_rtable.u.dst.path = &br->fake_rtable.u.dst;
> +
> INIT_LIST_HEAD(&br->age_list);
>
> br_stp_timer_init(br);
> diff --git a/net/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
> index bb90cd7..9d6a578 100644
> --- a/net/bridge/br_netfilter.c
> +++ b/net/bridge/br_netfilter.c
> @@ -101,33 +101,12 @@ static inline __be16 pppoe_proto(const struct sk_buff *skb)
> pppoe_proto(skb) == htons(PPP_IPV6) && \
> brnf_filter_pppoe_tagged)
>
> -/* We need these fake structures to make netfilter happy --
> - * lots of places assume that skb->dst != NULL, which isn't
> - * all that unreasonable.
> - *
> - * Currently, we fill in the PMTU entry because netfilter
> - * refragmentation needs it, and the rt_flags entry because
> - * ipt_REJECT needs it. Future netfilter modules might
> - * require us to fill additional fields. */
> -static struct net_device __fake_net_device = {
> - .hard_header_len = ETH_HLEN,
> -#ifdef CONFIG_NET_NS
> - .nd_net = &init_net,
> -#endif
> -};
> +static inline struct rtable *bridge_parent_rtable(const struct net_device *dev)
> +{
> + struct net_bridge_port *port = rcu_dereference(dev->br_port);
>
> -static struct rtable __fake_rtable = {
> - .u = {
> - .dst = {
> - .__refcnt = ATOMIC_INIT(1),
> - .dev = &__fake_net_device,
> - .path = &__fake_rtable.u.dst,
> - .metrics = {[RTAX_MTU - 1] = 1500},
> - .flags = DST_NOXFRM,
> - }
> - },
> - .rt_flags = 0,
> -};
> + return port ? &port->br->fake_rtable: &__fake_rtable;
> +}
port should always be non-null so the existing fake_rtable can
just go away no?
Also some of this could be #ifdef CONFIG_BRNETFILTER
--
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