udp, bpf: Ignore connections in reuseport group after BPF sk lookup

When BPF sk lookup invokes reuseport handling for the selected socket, it
should ignore the fact that reuseport group can contain connected UDP
sockets. With BPF sk lookup this is not relevant as we are not scoring
sockets to find the best match, which might be a connected UDP socket.

Fix it by unconditionally accepting the socket selected by reuseport.

This fixes the following two failures reported by test_progs.

  # ./test_progs -t sk_lookup
  ...
  #73/14 UDP IPv4 redir and reuseport with conns:FAIL
  ...
  #73/20 UDP IPv6 redir and reuseport with conns:FAIL
  ...

Fixes: a57066b1 ("Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net")
Reported-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200726120228.1414348-1-jakub@cloudflare.com

net/ipv4/udp.c

@@ -473,7 +473,7 @@ static struct sock *udp4_lookup_run_bpf(struct net *net,
 		return sk;
 
 	reuse_sk = lookup_reuseport(net, sk, skb, saddr, sport, daddr, hnum);
-	if (reuse_sk && !reuseport_has_conns(sk, false))
+	if (reuse_sk)
 		sk = reuse_sk;
 	return sk;
 }

net/ipv6/udp.c

@@ -208,7 +208,7 @@ static inline struct sock *udp6_lookup_run_bpf(struct net *net,
 		return sk;
 
 	reuse_sk = lookup_reuseport(net, sk, skb, saddr, sport, daddr, hnum);
-	if (reuse_sk && !reuseport_has_conns(sk, false))
+	if (reuse_sk)
 		sk = reuse_sk;
 	return sk;
 }