bpf: enforce TCP only support for sockmap

Only TCP sockets have been tested and at the moment the state change
callback only handles TCP sockets. This adds a check to ensure that
sockets actually being added are TCP sockets.

For net-next we can consider UDP support.
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

kernel/bpf/sockmap.c

@@ -840,6 +840,12 @@ static int sock_map_update_elem(struct bpf_map *map,
 		return -EINVAL;
 	}
 
+	if (skops.sk->sk_type != SOCK_STREAM ||
+	    skops.sk->sk_protocol != IPPROTO_TCP) {
+		fput(socket->file);
+		return -EOPNOTSUPP;
+	}
+
 	err = sock_map_ctx_update_elem(&skops, map, key, flags);
 	fput(socket->file);
 	return err;

tools/testing/selftests/bpf/test_maps.c

@@ -466,7 +466,7 @@ static void test_sockmap(int tasks, void *data)
 	int one = 1, map_fd_rx, map_fd_tx, map_fd_break, s, sc, rc;
 	struct bpf_map *bpf_map_rx, *bpf_map_tx, *bpf_map_break;
 	int ports[] = {50200, 50201, 50202, 50204};
-	int err, i, fd, sfd[6] = {0xdeadbeef};
+	int err, i, fd, udp, sfd[6] = {0xdeadbeef};
 	u8 buf[20] = {0x0, 0x5, 0x3, 0x2, 0x1, 0x0};
 	int parse_prog, verdict_prog;
 	struct sockaddr_in addr;
@@ -548,6 +548,16 @@ static void test_sockmap(int tasks, void *data)
 		goto out_sockmap;
 	}
 
+	/* Test update with unsupported UDP socket */
+	udp = socket(AF_INET, SOCK_DGRAM, 0);
+	i = 0;
+	err = bpf_map_update_elem(fd, &i, &udp, BPF_ANY);
+	if (!err) {
+		printf("Failed socket SOCK_DGRAM allowed '%i:%i'\n",
+		       i, udp);
+		goto out_sockmap;
+	}
+
 	/* Test update without programs */
 	for (i = 0; i < 6; i++) {
 		err = bpf_map_update_elem(fd, &i, &sfd[i], BPF_ANY);