net: Make locking in sock_bindtoindex optional

The sock_bindtoindex intended for kernel wide usage however
it will lock the socket regardless of the context. This modification
relax this behavior optionally: locking the socket will be optional
by calling the sock_bindtoindex with lock_sk = true.

The modification applied to all users of the sock_bindtoindex.
Signed-off-by: Ferenc Fejes <fejes@inf.elte.hu>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/bee6355da40d9e991b2f2d12b67d55ebb5f5b207.1590871065.git.fejes@inf.elte.hu

include/net/sock.h

@@ -2690,7 +2690,7 @@ static inline bool sk_dev_equal_l3scope(struct sock *sk, int dif)
 
 void sock_def_readable(struct sock *sk);
 
-int sock_bindtoindex(struct sock *sk, int ifindex);
+int sock_bindtoindex(struct sock *sk, int ifindex, bool lock_sk);
 void sock_enable_timestamps(struct sock *sk);
 void sock_no_linger(struct sock *sk);
 void sock_set_keepalive(struct sock *sk);

net/core/sock.c

@@ -594,13 +594,15 @@ static int sock_bindtoindex_locked(struct sock *sk, int ifindex)
 	return ret;
 }
 
-int sock_bindtoindex(struct sock *sk, int ifindex)
+int sock_bindtoindex(struct sock *sk, int ifindex, bool lock_sk)
 {
 	int ret;
 
-	lock_sock(sk);
+	if (lock_sk)
+		lock_sock(sk);
 	ret = sock_bindtoindex_locked(sk, ifindex);
-	release_sock(sk);
+	if (lock_sk)
+		release_sock(sk);
 
 	return ret;
 }
@@ -646,7 +648,7 @@ static int sock_setbindtodevice(struct sock *sk, char __user *optval,
 			goto out;
 	}
 
-	return sock_bindtoindex(sk, index);
+	return sock_bindtoindex(sk, index, true);
 out:
 #endif
 

net/ipv4/udp_tunnel.c

@@ -22,7 +22,7 @@ int udp_sock_create4(struct net *net, struct udp_port_cfg *cfg,
 		goto error;
 
 	if (cfg->bind_ifindex) {
-		err = sock_bindtoindex(sock->sk, cfg->bind_ifindex);
+		err = sock_bindtoindex(sock->sk, cfg->bind_ifindex, true);
 		if (err < 0)
 			goto error;
 	}

net/ipv6/ip6_udp_tunnel.c

@@ -30,7 +30,7 @@ int udp_sock_create6(struct net *net, struct udp_port_cfg *cfg,
 			goto error;
 	}
 	if (cfg->bind_ifindex) {
-		err = sock_bindtoindex(sock->sk, cfg->bind_ifindex);
+		err = sock_bindtoindex(sock->sk, cfg->bind_ifindex, true);
 		if (err < 0)
 			goto error;
 	}