Re: [PATCH net v3] skbuff: Release nfct refcount on napi stolen or re-used skbs

[Florian Fainelli <f.fainelli@gmail.com>]

On 7/5/2021 3:54 AM, Paul Blakey wrote:
> When multiple SKBs are merged to a new skb under napi GRO,
> or SKB is re-used by napi, if nfct was set for them in the
> driver, it will not be released while freeing their stolen
> head state or on re-use.
> 
> Release nfct on napi's stolen or re-used SKBs, and
> in gro_list_prepare, check conntrack metadata diff.
> 
> Fixes: 5c6b94604744 ("net/mlx5e: CT: Handle misses after executing CT action")
> Reviewed-by: Roi Dayan <roid@nvidia.com>
> Signed-off-by: Paul Blakey <paulb@nvidia.com>

FWIW this change broke builds with CONFIG_SKB_EXTENSIONS disabled and 
also does not guard against CONFIG_NET_TC_SKB_EXT being disabled as well:

   CC      net/core/dev.o
net/core/dev.c: In function 'gro_list_prepare':
net/core/dev.c:6015:33: error: implicit declaration of function 
'skb_ext_find'; did you mean 'skb_ext_copy'? 
[-Werror=implicit-function-declaration]
     struct tc_skb_ext *skb_ext = skb_ext_find(skb, TC_SKB_EXT);
                                  ^~~~~~~~~~~~
                                  skb_ext_copy
net/core/dev.c:6015:51: error: 'TC_SKB_EXT' undeclared (first use in 
this function); did you mean 'TC_U32_EAT'?
     struct tc_skb_ext *skb_ext = skb_ext_find(skb, TC_SKB_EXT);
                                                    ^~~~~~~~~~
                                                    TC_U32_EAT
net/core/dev.c:6015:51: note: each undeclared identifier is reported 
only once for each function it appears in
net/core/dev.c:6020:19: error: dereferencing pointer to incomplete type 
'struct tc_skb_ext'
      diffs |= p_ext->chain ^ skb_ext->chain;
                    ^~
cc1: some warnings being treated as errors
make[2]: *** [scripts/Makefile.build:273: net/core/dev.o] Error 1
make[1]: *** [scripts/Makefile.build:516: net/core] Error 2
make: *** [Makefile:1847: net] Error 2

Fix: 
https://lore.kernel.org/netdev/20210708041051.17851-1-f.fainelli@gmail.com/

> ---
> Changelog:
> 	v2->v1:
> 	 in napi_skb_free_stolen_head() use nf_reset_ct(skb) instead, so we also zero nfct ptr.
> 	v1->v2:
> 	 Check for different flows based on CT and chain metadata in gro_list_prepare
> 
>   net/core/dev.c    | 13 +++++++++++++
>   net/core/skbuff.c |  1 +
>   2 files changed, 14 insertions(+)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 439faadab0c2..bf62cb2ec6da 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -5981,6 +5981,18 @@ static void gro_list_prepare(const struct list_head *head,
>   			diffs = memcmp(skb_mac_header(p),
>   				       skb_mac_header(skb),
>   				       maclen);
> +
> +		diffs |= skb_get_nfct(p) ^ skb_get_nfct(skb);
> +
> +		if (!diffs) {
> +			struct tc_skb_ext *skb_ext = skb_ext_find(skb, TC_SKB_EXT);
> +			struct tc_skb_ext *p_ext = skb_ext_find(p, TC_SKB_EXT);
> +
> +			diffs |= (!!p_ext) ^ (!!skb_ext);
> +			if (!diffs && unlikely(skb_ext))
> +				diffs |= p_ext->chain ^ skb_ext->chain;
> +		}
> +
>   		NAPI_GRO_CB(p)->same_flow = !diffs;
>   	}
>   }
> @@ -6243,6 +6255,7 @@ static void napi_reuse_skb(struct napi_struct *napi, struct sk_buff *skb)
>   	skb_shinfo(skb)->gso_type = 0;
>   	skb->truesize = SKB_TRUESIZE(skb_end_offset(skb));
>   	skb_ext_reset(skb);
> +	nf_reset_ct(skb);
>   
>   	napi->skb = skb;
>   }
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index bbc3b4b62032..30ca61d91b69 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -939,6 +939,7 @@ void __kfree_skb_defer(struct sk_buff *skb)
>   
>   void napi_skb_free_stolen_head(struct sk_buff *skb)
>   {
> +	nf_reset_ct(skb);
>   	skb_dst_drop(skb);
>   	skb_ext_put(skb);
>   	napi_skb_cache_put(skb);
> 

-- 
Florian