Re: [PATCH net-next v4 2/4] net: ipv6: ioam6_iptunnel: mitigate 2-realloc issue

From: Paolo Abeni
Date: Tue Nov 19 2024 - 05:42:48 EST


On 11/18/24 14:15, Justin Iurman wrote:
> @@ -387,45 +392,40 @@ static int ioam6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
> goto drop;
> }
>
> - err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
> - if (unlikely(err))
> - goto drop;
> + if (unlikely(!dst)) {
> + struct ipv6hdr *hdr = ipv6_hdr(skb);
> + struct flowi6 fl6;
> +
> + memset(&fl6, 0, sizeof(fl6));
> + fl6.daddr = hdr->daddr;
> + fl6.saddr = hdr->saddr;
> + fl6.flowlabel = ip6_flowinfo(hdr);
> + fl6.flowi6_mark = skb->mark;
> + fl6.flowi6_proto = hdr->nexthdr;
> +
> + dst = ip6_route_output(net, NULL, &fl6);
> + if (dst->error) {
> + err = dst->error;
> + dst_release(dst);
> + goto drop;
> + }
>
> - if (!ipv6_addr_equal(&orig_daddr, &ipv6_hdr(skb)->daddr)) {
> local_bh_disable();
> - dst = dst_cache_get(&ilwt->cache);
> + dst_cache_set_ip6(&ilwt->cache, dst, &fl6.saddr);
> local_bh_enable();
>
> - if (unlikely(!dst)) {
> - struct ipv6hdr *hdr = ipv6_hdr(skb);
> - struct flowi6 fl6;
> -
> - memset(&fl6, 0, sizeof(fl6));
> - fl6.daddr = hdr->daddr;
> - fl6.saddr = hdr->saddr;
> - fl6.flowlabel = ip6_flowinfo(hdr);
> - fl6.flowi6_mark = skb->mark;
> - fl6.flowi6_proto = hdr->nexthdr;
> -
> - dst = ip6_route_output(net, NULL, &fl6);
> - if (dst->error) {
> - err = dst->error;
> - dst_release(dst);
> - goto drop;
> - }
> -
> - local_bh_disable();
> - dst_cache_set_ip6(&ilwt->cache, dst, &fl6.saddr);
> - local_bh_enable();
> - }
> + err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
> + if (unlikely(err))
> + goto drop;
> + }
>
> - skb_dst_drop(skb);
> - skb_dst_set(skb, dst);
> + skb_dst_drop(skb);
> + skb_dst_set(skb, dst);

Why the above 2 statements are not done only in case of ip address
match, as in the existing code?

>
> + if (!ipv6_addr_equal(&orig_daddr, &ipv6_hdr(skb)->daddr))
> return dst_output(net, sk, skb);
> - }


Thanks,

Paolo