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Hello,
On Mon, 24 Oct 2016, Dwip Banerjee wrote:
> We decrement the IP ttl in all the modes in order to prevent infinite
> route loops. The changes were done based on Julian Anastasov's
> suggestions in a prior thread.
>
> The ttl based check/discard and the actual decrement are done in
> __ip_vs_get_out_rt() and in __ip_vs_get_out_rt_v6(), for the IPv6
> case. decrement_ttl() implements the actual functionality for the
> two cases.
>
>
> Signed-off-by: Dwip Banerjee <dwip@xxxxxxxxxxxxxxxxxx>
> ---
> net/netfilter/ipvs/ip_vs_xmit.c | 55
> +++++++++++++++++++++++++++++++++++++++
> 1 files changed, 55 insertions(+), 0 deletions(-)
>
> diff --git a/net/netfilter/ipvs/ip_vs_xmit.c b/net/netfilter/ipvs/ip_vs_xmit.c
> index 01d3d89..8b11e92 100644
> --- a/net/netfilter/ipvs/ip_vs_xmit.c
> +++ b/net/netfilter/ipvs/ip_vs_xmit.c
> @@ -254,6 +254,55 @@ static inline bool ensure_mtu_is_adequate(struct
> netns_ipvs *ipvs, int skb_af,
> return true;
> }
>
> +static inline bool decrement_ttl(int skb_af, struct sk_buff *skb)
> +{
> +#ifdef CONFIG_IP_VS_IPV6
> + if (skb_af == AF_INET6) {
> + struct ipv6hdr *hdr = ipv6_hdr(skb);
> + struct dst_entry *dst = skb_dst(skb);
> + struct net *net = dev_net(dst->dev);
dev_net should not be used anymore, you can check
the latest changes by Eric W. Biederman:
git log -p -- net/netfilter/ipvs/ip_vs_xmit.c
Better to use ipvs->net.
> +
> + /* check and decrement ttl */
> + if (hdr->hop_limit <= 1) {
> + /* Force OUTPUT device used as source address */
> + skb->dev = dst->dev;
> + icmpv6_send(skb, ICMPV6_TIME_EXCEED,
> + ICMPV6_EXC_HOPLIMIT, 0);
> + __IP6_INC_STATS(net, ip6_dst_idev(dst),
> + IPSTATS_MIB_INHDRERRORS);
> +
> + return false;
> + }
> +
> + /* don't propagate ttl change to cloned packets */
> + if (!skb_make_writable(skb, sizeof(struct ipv6hdr)))
> + return false;
Now I see that using hdr after skb_make_writable is
risky because skb data can be reallocated. Better to use
ip[v6]_hdr(skb) for all places, i.e. without any hdr/iph ptrs.
> +
> + hdr->hop_limit--;
> + } else
> +#endif
> + {
> + struct iphdr *iph = ip_hdr(skb);
> +
> + if (iph->ttl <= 1) {
> + /* Tell the sender its packet died... */
> + __IP_INC_STATS(dev_net(skb_dst(skb)->dev),
> + IPSTATS_MIB_INHDRERRORS);
> + icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
> + return false;
> + }
> +
> + /* don't propagate ttl change to cloned packets */
> + if (!skb_make_writable(skb, sizeof(struct iphdr)))
> + return false;
> +
> + /* Decrease ttl */
> + ip_decrease_ttl(iph);
> + }
> +
> + return true;
> +}
> +
Regards
--
Julian Anastasov <ja@xxxxxx>
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