hello wenxu!
On Thu, 2020-11-05 at 18:41 +0800, we...@ucloud.cn wrote:
> From: wenxu <we...@ucloud.cn>
>
> Currently kernel tc subsystem can do conntrack in act_ct. But when several
> fragment packets go through the act_ct, function tcf_ct_handle_fragments
> will defrag the packets to a big one. But the last action will redirect
> mirred to a device which maybe lead the reassembly big packet over the mtu
> of target device.
>
> This patch add support for a xmit hook to mirred, that gets executed before
> xmiting the packet. Then, when act_ct gets loaded, it configs that hook.
> The frag xmit hook maybe reused by other modules.
>
> Signed-off-by: wenxu <we...@ucloud.cn>
> ---
[...]
> +
> +static int tcf_fragment(struct net *net, struct sk_buff *skb,
> + u16 mru, int (*xmit)(struct sk_buff *skb))
> +{
> + if (skb_network_offset(skb) > VLAN_ETH_HLEN) {
> + net_warn_ratelimited("L2 header too long to fragment\n");
> + goto err;
> + }
> +
> + if (skb->protocol == htons(ETH_P_IP)) {
small nit: use of skb->protocol here may lead to "ambiguous" results: a
VLAN "accelerated" packet is properly processed, while the same VLAN
packet with "non-accelerated" tag is not processed because skb->protocol
is htons(ETH_P_8021Q). Can I suggest use of skb_protocol(), that has
been introduced recently by Toke [1] ?
> + ip_do_fragment(net, skb->sk, skb, tcf_frag_xmit);
> + refdst_drop(orig_dst);
> + } else if (skb->protocol == htons(ETH_P_IPV6)) {
same here,
> + unsigned long orig_dst;
> + struct rt6_info tcf_frag_rt;
> +
> + tcf_frag_prepare_frag(skb, xmit);
> + memset(&tcf_frag_rt, 0, sizeof(tcf_frag_rt));
> + dst_init(&tcf_frag_rt.dst, &tcf_frag_dst_ops, NULL, 1,
> + DST_OBSOLETE_NONE, DST_NOCOUNT);
> + tcf_frag_rt.dst.dev = skb->dev;
> +
> + orig_dst = skb->_skb_refdst;
> + skb_dst_set_noref(skb, &tcf_frag_rt.dst);
> + IP6CB(skb)->frag_max_size = mru;
> +
> + ipv6_stub->ipv6_fragment(net, skb->sk, skb, tcf_frag_xmit);
> + refdst_drop(orig_dst);
> + } else {
> + net_warn_ratelimited("Failed fragment ->%s: eth=%04x, MRU=%d,
> MTU=%d.\n",
> + netdev_name(skb->dev),
> ntohs(skb->protocol),
> + mru, skb->dev->mtu);
and here (even though it's just a printout).
thanks!
--
davide
[1] https://lore.kernel.org/netdev/20200707110325.86731-1-t...@redhat.com/
