Subject: Re: [PATCH bpf,v3 3/4] bpf: fix bpf socket lookup from tc/xdp to respect socket VRF bindings

From: Stanislav Fomichev <[email-masked]>
Date: Thu, 27 Apr 2023 11:03:27 -0700

On 04/26, Gilad Sever wrote:
> When calling bpf_sk_lookup_tcp(), bpf_sk_lookup_udp() or
> bpf_skc_lookup_tcp() from tc/xdp ingress, VRF socket bindings aren't
> respoected, i.e. unbound sockets are returned, and bound sockets aren't
> found.
> 
> VRF binding is determined by the sdif argument to sk_lookup(), however
> when called from tc the IP SKB control block isn't initialized and thus
> inet{,6}_sdif() always returns 0.
> 
> Fix by calculating sdif for the tc/xdp flows by observing the device's
> l3 enslaved state.
> 
> The cg/sk_skb hooking points which are expected to support
> inet{,6}_sdif() pass sdif=-1 which makes __bpf_skc_lookup() use the
> existing logic.
> 
> Fixes: 6acc9b432e67 ("bpf: Add helper to retrieve socket in BPF")
> Reviewed-by: Shmulik Ladkani <[email-masked]>
> Reviewed-by: Eyal Birger <[email-masked]>
> Signed-off-by: Gilad Sever <[email-masked]>

Acked-by: Stanislav Fomichev <[email-masked]>

with one nit below

> ---
> v3: Rename bpf_l2_sdif() to dev_sdif() as suggested by Stanislav Fomichev
> ---
>  net/core/filter.c | 63 +++++++++++++++++++++++++++++++----------------
>  1 file changed, 42 insertions(+), 21 deletions(-)
> 
> diff --git a/net/core/filter.c b/net/core/filter.c
> index f43f86fc1235..894913aaa29f 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -6529,12 +6529,11 @@ static struct sock *sk_lookup(struct net *net, struct bpf_sock_tuple *tuple,
>  static struct sock *
>  __bpf_skc_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len,
>  		 struct net *caller_net, u32 ifindex, u8 proto, u64 netns_id,
> -		 u64 flags)
> +		 u64 flags, int sdif)
>  {
>  	struct sock *sk = NULL;
>  	struct net *net;
>  	u8 family;
> -	int sdif;
>  
>  	if (len == sizeof(tuple->ipv4))
>  		family = AF_INET;
> @@ -6546,10 +6545,12 @@ __bpf_skc_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len,
>  	if (unlikely(flags || !((s32)netns_id < 0 || netns_id <= S32_MAX)))
>  		goto out;
>  
> -	if (family == AF_INET)
> -		sdif = inet_sdif(skb);
> -	else
> -		sdif = inet6_sdif(skb);
> +	if (sdif < 0) {
> +		if (family == AF_INET)
> +			sdif = inet_sdif(skb);
> +		else
> +			sdif = inet6_sdif(skb);
> +	}
>  
>  	if ((s32)netns_id < 0) {
>  		net = caller_net;
> @@ -6569,10 +6570,11 @@ __bpf_skc_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len,
>  static struct sock *
>  __bpf_sk_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len,
>  		struct net *caller_net, u32 ifindex, u8 proto, u64 netns_id,
> -		u64 flags)
> +		u64 flags, int sdif)
>  {
>  	struct sock *sk = __bpf_skc_lookup(skb, tuple, len, caller_net,
> -					   ifindex, proto, netns_id, flags);
> +					   ifindex, proto, netns_id, flags,
> +					   sdif);
>  
>  	if (sk) {
>  		struct sock *sk2 = sk_to_full_sk(sk);
> @@ -6612,7 +6614,7 @@ bpf_skc_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len,
>  	}
>  
>  	return __bpf_skc_lookup(skb, tuple, len, caller_net, ifindex, proto,
> -				netns_id, flags);
> +				netns_id, flags, -1);
>  }
>  
>  static struct sock *
> @@ -6701,15 +6703,25 @@ static const struct bpf_func_proto bpf_sk_lookup_udp_proto = {
>  	.arg5_type	= ARG_ANYTHING,
>  };

[..]

> +static int dev_sdif(const struct net_device *dev)
> +{
> +#if IS_ENABLED(CONFIG_NET_L3_MASTER_DEV)
> +	if (netif_is_l3_slave(dev))
> +		return dev->ifindex;
> +#endif
> +	return 0;
> +}

nit: should this go into include/linux/netdevice.h?

> +
>  BPF_CALL_5(bpf_tc_skc_lookup_tcp, struct sk_buff *, skb,
>  	   struct bpf_sock_tuple *, tuple, u32, len, u64, netns_id, u64, flags)
>  {
>  	struct net *caller_net = dev_net(skb->dev);
> +	int sdif = dev_sdif(skb->dev);
>  	int ifindex = skb->dev->ifindex;
>  
>  	return (unsigned long)__bpf_skc_lookup(skb, tuple, len, caller_net,
>  					       ifindex, IPPROTO_TCP, netns_id,
> -					       flags);
> +					       flags, sdif);
>  }
>  
>  static const struct bpf_func_proto bpf_tc_skc_lookup_tcp_proto = {
> @@ -6728,11 +6740,12 @@ BPF_CALL_5(bpf_tc_sk_lookup_tcp, struct sk_buff *, skb,
>  	   struct bpf_sock_tuple *, tuple, u32, len, u64, netns_id, u64, flags)
>  {
>  	struct net *caller_net = dev_net(skb->dev);
> +	int sdif = dev_sdif(skb->dev);
>  	int ifindex = skb->dev->ifindex;
>  
>  	return (unsigned long)__bpf_sk_lookup(skb, tuple, len, caller_net,
>  					      ifindex, IPPROTO_TCP, netns_id,
> -					      flags);
> +					      flags, sdif);
>  }
>  
>  static const struct bpf_func_proto bpf_tc_sk_lookup_tcp_proto = {
> @@ -6751,11 +6764,12 @@ BPF_CALL_5(bpf_tc_sk_lookup_udp, struct sk_buff *, skb,
>  	   struct bpf_sock_tuple *, tuple, u32, len, u64, netns_id, u64, flags)
>  {
>  	struct net *caller_net = dev_net(skb->dev);
> +	int sdif = dev_sdif(skb->dev);
>  	int ifindex = skb->dev->ifindex;
>  
>  	return (unsigned long)__bpf_sk_lookup(skb, tuple, len, caller_net,
>  					      ifindex, IPPROTO_UDP, netns_id,
> -					      flags);
> +					      flags, sdif);
>  }
>  
>  static const struct bpf_func_proto bpf_tc_sk_lookup_udp_proto = {
> @@ -6788,11 +6802,13 @@ BPF_CALL_5(bpf_xdp_sk_lookup_udp, struct xdp_buff *, ctx,
>  	   struct bpf_sock_tuple *, tuple, u32, len, u32, netns_id, u64, flags)
>  {
>  	struct net *caller_net = dev_net(ctx->rxq->dev);
> -	int ifindex = ctx->rxq->dev->ifindex;
> +	struct net_device *dev = ctx->rxq->dev;
> +	int sdif = dev_sdif(dev);
> +	int ifindex = dev->ifindex;
>  
>  	return (unsigned long)__bpf_sk_lookup(NULL, tuple, len, caller_net,
>  					      ifindex, IPPROTO_UDP, netns_id,
> -					      flags);
> +					      flags, sdif);
>  }
>  
>  static const struct bpf_func_proto bpf_xdp_sk_lookup_udp_proto = {
> @@ -6811,11 +6827,13 @@ BPF_CALL_5(bpf_xdp_skc_lookup_tcp, struct xdp_buff *, ctx,
>  	   struct bpf_sock_tuple *, tuple, u32, len, u32, netns_id, u64, flags)
>  {
>  	struct net *caller_net = dev_net(ctx->rxq->dev);
> -	int ifindex = ctx->rxq->dev->ifindex;
> +	struct net_device *dev = ctx->rxq->dev;
> +	int sdif = dev_sdif(dev);
> +	int ifindex = dev->ifindex;
>  
>  	return (unsigned long)__bpf_skc_lookup(NULL, tuple, len, caller_net,
>  					       ifindex, IPPROTO_TCP, netns_id,
> -					       flags);
> +					       flags, sdif);
>  }
>  
>  static const struct bpf_func_proto bpf_xdp_skc_lookup_tcp_proto = {
> @@ -6834,11 +6852,13 @@ BPF_CALL_5(bpf_xdp_sk_lookup_tcp, struct xdp_buff *, ctx,
>  	   struct bpf_sock_tuple *, tuple, u32, len, u32, netns_id, u64, flags)
>  {
>  	struct net *caller_net = dev_net(ctx->rxq->dev);
> -	int ifindex = ctx->rxq->dev->ifindex;
> +	struct net_device *dev = ctx->rxq->dev;
> +	int sdif = dev_sdif(dev);
> +	int ifindex = dev->ifindex;
>  
>  	return (unsigned long)__bpf_sk_lookup(NULL, tuple, len, caller_net,
>  					      ifindex, IPPROTO_TCP, netns_id,
> -					      flags);
> +					      flags, sdif);
>  }
>  
>  static const struct bpf_func_proto bpf_xdp_sk_lookup_tcp_proto = {
> @@ -6858,7 +6878,8 @@ BPF_CALL_5(bpf_sock_addr_skc_lookup_tcp, struct bpf_sock_addr_kern *, ctx,
>  {
>  	return (unsigned long)__bpf_skc_lookup(NULL, tuple, len,
>  					       sock_net(ctx->sk), 0,
> -					       IPPROTO_TCP, netns_id, flags);
> +					       IPPROTO_TCP, netns_id, flags,
> +					       -1);
>  }
>  
>  static const struct bpf_func_proto bpf_sock_addr_skc_lookup_tcp_proto = {
> @@ -6877,7 +6898,7 @@ BPF_CALL_5(bpf_sock_addr_sk_lookup_tcp, struct bpf_sock_addr_kern *, ctx,
>  {
>  	return (unsigned long)__bpf_sk_lookup(NULL, tuple, len,
>  					      sock_net(ctx->sk), 0, IPPROTO_TCP,
> -					      netns_id, flags);
> +					      netns_id, flags, -1);
>  }
>  
>  static const struct bpf_func_proto bpf_sock_addr_sk_lookup_tcp_proto = {
> @@ -6896,7 +6917,7 @@ BPF_CALL_5(bpf_sock_addr_sk_lookup_udp, struct bpf_sock_addr_kern *, ctx,
>  {
>  	return (unsigned long)__bpf_sk_lookup(NULL, tuple, len,
>  					      sock_net(ctx->sk), 0, IPPROTO_UDP,
> -					      netns_id, flags);
> +					      netns_id, flags, -1);
>  }
>  
>  static const struct bpf_func_proto bpf_sock_addr_sk_lookup_udp_proto = {
> -- 
> 2.34.1
>