netdev - Re: [PATCH net 2/2] net: ipv6: fix dst ref loops in rpl, seg6 and ioam6 lwtunnels

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Message-ID: <4a30a0aa-2893-4f6a-a858-61e51b2430b2@uliege.be>
Date: Wed, 29 Jan 2025 17:50:14 +0100
From: Justin Iurman <justin.iurman@...ege.be>
To: Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net
Cc: netdev@...r.kernel.org, edumazet@...gle.com, pabeni@...hat.com,
 andrew+netdev@...n.ch, horms@...nel.org, dsahern@...nel.org
Subject: Re: [PATCH net 2/2] net: ipv6: fix dst ref loops in rpl, seg6 and
 ioam6 lwtunnels

On 1/29/25 03:13, Jakub Kicinski wrote:
> Some lwtunnels have a dst cache for post-transformation dst.
> If the packet destination did not change we may end up recording
> a reference to the lwtunnel in its own cache, and the lwtunnel
> state will never be freed.
> 
> Discovered by the ioam6.sh test, kmemleak was recently fixed
> to catch per-cpu memory leaks. I'm not sure if rpl and seg6
> can actually hit this, but in principle I don't see why not.

Agree, both can theoretically hit this too.

> Fixes: 985ec6f5e623 ("net: ipv6: rpl_iptunnel: mitigate 2-realloc issue")
> Fixes: 40475b63761a ("net: ipv6: seg6_iptunnel: mitigate 2-realloc issue")
> Fixes: dce525185bc9 ("net: ipv6: ioam6_iptunnel: mitigate 2-realloc issue")
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> ---
> CC: dsahern@...nel.org
> CC: justin.iurman@...ege.be
> ---
>   net/ipv6/ioam6_iptunnel.c | 9 ++++++---
>   net/ipv6/rpl_iptunnel.c   | 9 ++++++---
>   net/ipv6/seg6_iptunnel.c  | 9 ++++++---
>   3 files changed, 18 insertions(+), 9 deletions(-)
> 
> diff --git a/net/ipv6/ioam6_iptunnel.c b/net/ipv6/ioam6_iptunnel.c
> index 3936c137a572..0279f1327ad5 100644
> --- a/net/ipv6/ioam6_iptunnel.c
> +++ b/net/ipv6/ioam6_iptunnel.c
> @@ -410,9 +410,12 @@ static int ioam6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>   			goto drop;
>   		}
>   
> -		local_bh_disable();
> -		dst_cache_set_ip6(&ilwt->cache, cache_dst, &fl6.saddr);
> -		local_bh_enable();
> +		/* cache only if we don't create a dst refrence loop */

s/refrence/reference

> +		if (dst->lwtstate != cache_dst->lwtstate) {
> +			local_bh_disable();
> +			dst_cache_set_ip6(&ilwt->cache, cache_dst, &fl6.saddr);
> +			local_bh_enable();
> +		}

I agree the above patch fixes what kmemleak reported. However, I think 
it'd bring the double-reallocation issue back when the packet 
destination did not change (i.e., cache will always be empty). I'll try 
to come up with a solution...

>   
>   		err = skb_cow_head(skb, LL_RESERVED_SPACE(cache_dst->dev));
>   		if (unlikely(err))
> diff --git a/net/ipv6/rpl_iptunnel.c b/net/ipv6/rpl_iptunnel.c
> index 9b7d03563115..f3febe4881a5 100644
> --- a/net/ipv6/rpl_iptunnel.c
> +++ b/net/ipv6/rpl_iptunnel.c
> @@ -235,9 +235,12 @@ static int rpl_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>   			goto drop;
>   		}
>   
> -		local_bh_disable();
> -		dst_cache_set_ip6(&rlwt->cache, dst, &fl6.saddr);
> -		local_bh_enable();
> +		/* cache only if we don't create a dst refrence loop */

s/refrence/reference

Same comment as above.

> +		if (orig_dst->lwtstate != dst->lwtstate) {
> +			local_bh_disable();
> +			dst_cache_set_ip6(&rlwt->cache, dst, &fl6.saddr);
> +			local_bh_enable();
> +		}
>   
>   		err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
>   		if (unlikely(err))
> diff --git a/net/ipv6/seg6_iptunnel.c b/net/ipv6/seg6_iptunnel.c
> index eacc4e91b48e..0da989f07376 100644
> --- a/net/ipv6/seg6_iptunnel.c
> +++ b/net/ipv6/seg6_iptunnel.c
> @@ -576,9 +576,12 @@ static int seg6_output_core(struct net *net, struct sock *sk,
>   			goto drop;
>   		}
>   
> -		local_bh_disable();
> -		dst_cache_set_ip6(&slwt->cache, dst, &fl6.saddr);
> -		local_bh_enable();
> +		/* cache only if we don't create a dst refrence loop */

s/refrence/reference

Same comment as above.

> +		if (orig_dst->lwtstate != dst->lwtstate) {
> +			local_bh_disable();
> +			dst_cache_set_ip6(&slwt->cache, dst, &fl6.saddr);
> +			local_bh_enable();
> +		}
>   
>   		err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
>   		if (unlikely(err))