bpf, sockmap: SK_DROP on attempted redirects of unsupported af_vsock

Don't mislead the callers of bpf_{sk,msg}_redirect_{map,hash}(): make sure
to immediately and visibly fail the forwarding of unsupported af_vsock
packets.

Fixes: 634f1a7 ("vsock: support sockmap")
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20241013-vsock-fixes-for-redir-v2-1-d6577bbfe742@rbox.co

Author: mmhal

include/net/sock.h

@@ -2715,6 +2715,11 @@ static inline bool sk_is_stream_unix(const struct sock *sk)
 	return sk->sk_family == AF_UNIX && sk->sk_type == SOCK_STREAM;
 }
 
+static inline bool sk_is_vsock(const struct sock *sk)
+{
+	return sk->sk_family == AF_VSOCK;
+}
+
 /**
  * sk_eat_skb - Release a skb if it is no longer needed
  * @sk: socket to eat this skb from

net/core/sock_map.c

@@ -647,6 +647,8 @@ BPF_CALL_4(bpf_sk_redirect_map, struct sk_buff *, skb,
 	sk = __sock_map_lookup_elem(map, key);
 	if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
 		return SK_DROP;
+	if ((flags & BPF_F_INGRESS) && sk_is_vsock(sk))
+		return SK_DROP;
 
 	skb_bpf_set_redir(skb, sk, flags & BPF_F_INGRESS);
 	return SK_PASS;
@@ -675,6 +677,8 @@ BPF_CALL_4(bpf_msg_redirect_map, struct sk_msg *, msg,
 		return SK_DROP;
 	if (!(flags & BPF_F_INGRESS) && !sk_is_tcp(sk))
 		return SK_DROP;
+	if (sk_is_vsock(sk))
+		return SK_DROP;
 
 	msg->flags = flags;
 	msg->sk_redir = sk;
@@ -1249,6 +1253,8 @@ BPF_CALL_4(bpf_sk_redirect_hash, struct sk_buff *, skb,
 	sk = __sock_hash_lookup_elem(map, key);
 	if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
 		return SK_DROP;
+	if ((flags & BPF_F_INGRESS) && sk_is_vsock(sk))
+		return SK_DROP;
 
 	skb_bpf_set_redir(skb, sk, flags & BPF_F_INGRESS);
 	return SK_PASS;
@@ -1277,6 +1283,8 @@ BPF_CALL_4(bpf_msg_redirect_hash, struct sk_msg *, msg,
 		return SK_DROP;
 	if (!(flags & BPF_F_INGRESS) && !sk_is_tcp(sk))
 		return SK_DROP;
+	if (sk_is_vsock(sk))
+		return SK_DROP;
 
 	msg->flags = flags;
 	msg->sk_redir = sk;