Re: [PATCH net v2 1/2] seg6: separate dst_cache for input and output paths in seg6 lwtunnel

[Justin Iurman <justin.iurman@gmail.com>]

On 4/1/26 20:57, Andrea Mayer wrote:
> The seg6 lwtunnel uses a single dst_cache per encap route, shared
> between seg6_input_core() and seg6_output_core(). These two paths
> can perform the post-encap SID lookup in different routing contexts
> (e.g., ip rules matching on the ingress interface, or VRF table
> separation). Whichever path runs first populates the cache, and the
> other reuses it blindly, bypassing its own lookup.
> 
> Fix this by splitting the cache into cache_input and cache_output,
> so each path maintains its own cached dst independently.
> 
> Fixes: 6c8702c60b88 ("ipv6: sr: add support for SRH encapsulation and injection with lwtunnels")
> Cc: stable@vger.kernel.org
> Signed-off-by: Andrea Mayer <andrea.mayer@uniroma2.it>
> Reviewed-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
> ---
>   net/ipv6/seg6_iptunnel.c | 34 +++++++++++++++++++++++-----------
>   1 file changed, 23 insertions(+), 11 deletions(-)
> 
> diff --git a/net/ipv6/seg6_iptunnel.c b/net/ipv6/seg6_iptunnel.c
> index 3e1b9991131a..d6a0f7df9080 100644
> --- a/net/ipv6/seg6_iptunnel.c
> +++ b/net/ipv6/seg6_iptunnel.c
> @@ -48,7 +48,8 @@ static size_t seg6_lwt_headroom(struct seg6_iptunnel_encap *tuninfo)
>   }
>   
>   struct seg6_lwt {
> -	struct dst_cache cache;
> +	struct dst_cache cache_input;
> +	struct dst_cache cache_output;
>   	struct seg6_iptunnel_encap tuninfo[];
>   };
>   
> @@ -488,7 +489,7 @@ static int seg6_input_core(struct net *net, struct sock *sk,
>   	slwt = seg6_lwt_lwtunnel(lwtst);
>   
>   	local_bh_disable();
> -	dst = dst_cache_get(&slwt->cache);
> +	dst = dst_cache_get(&slwt->cache_input);
>   	local_bh_enable();
>   
>   	err = seg6_do_srh(skb, dst);
> @@ -504,7 +505,7 @@ static int seg6_input_core(struct net *net, struct sock *sk,
>   		/* cache only if we don't create a dst reference loop */
>   		if (!dst->error && lwtst != dst->lwtstate) {
>   			local_bh_disable();
> -			dst_cache_set_ip6(&slwt->cache, dst,
> +			dst_cache_set_ip6(&slwt->cache_input, dst,
>   					  &ipv6_hdr(skb)->saddr);
>   			local_bh_enable();
>   		}
> @@ -564,7 +565,7 @@ static int seg6_output_core(struct net *net, struct sock *sk,
>   	slwt = seg6_lwt_lwtunnel(orig_dst->lwtstate);
>   
>   	local_bh_disable();
> -	dst = dst_cache_get(&slwt->cache);
> +	dst = dst_cache_get(&slwt->cache_output);
>   	local_bh_enable();
>   
>   	err = seg6_do_srh(skb, dst);
> @@ -591,7 +592,7 @@ static int seg6_output_core(struct net *net, struct sock *sk,
>   		/* cache only if we don't create a dst reference loop */
>   		if (orig_dst->lwtstate != dst->lwtstate) {
>   			local_bh_disable();
> -			dst_cache_set_ip6(&slwt->cache, dst, &fl6.saddr);
> +			dst_cache_set_ip6(&slwt->cache_output, dst, &fl6.saddr);
>   			local_bh_enable();
>   		}
>   
> @@ -701,11 +702,13 @@ static int seg6_build_state(struct net *net, struct nlattr *nla,
>   
>   	slwt = seg6_lwt_lwtunnel(newts);
>   
> -	err = dst_cache_init(&slwt->cache, GFP_ATOMIC);
> -	if (err) {
> -		kfree(newts);
> -		return err;
> -	}
> +	err = dst_cache_init(&slwt->cache_input, GFP_ATOMIC);
> +	if (err)
> +		goto err_free_newts;
> +
> +	err = dst_cache_init(&slwt->cache_output, GFP_ATOMIC);
> +	if (err)
> +		goto err_destroy_input;
>   
>   	memcpy(&slwt->tuninfo, tuninfo, tuninfo_len);
>   
> @@ -720,11 +723,20 @@ static int seg6_build_state(struct net *net, struct nlattr *nla,
>   	*ts = newts;
>   
>   	return 0;
> +
> +err_destroy_input:
> +	dst_cache_destroy(&slwt->cache_input);
> +err_free_newts:
> +	kfree(newts);
> +	return err;
>   }
>   
>   static void seg6_destroy_state(struct lwtunnel_state *lwt)
>   {
> -	dst_cache_destroy(&seg6_lwt_lwtunnel(lwt)->cache);
> +	struct seg6_lwt *slwt = seg6_lwt_lwtunnel(lwt);
> +
> +	dst_cache_destroy(&slwt->cache_input);
> +	dst_cache_destroy(&slwt->cache_output);
>   }
>   
>   static int seg6_fill_encap_info(struct sk_buff *skb,

Reviewed-by: Justin Iurman <justin.iurman@gmail.com>