inet: implement lockless getsockopt(IP_UNICAST_IF)

Add missing READ_ONCE() annotations when reading inet->uc_index

Implementing getsockopt(IP_UNICAST_IF) locklessly seems possible,
the setsockopt() part might not be possible at the moment.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/datagram.c

@@ -43,7 +43,7 @@ int __ip4_datagram_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len
 		if (!saddr)
 			saddr = inet->mc_addr;
 	} else if (!oif) {
-		oif = inet->uc_index;
+		oif = READ_ONCE(inet->uc_index);
 	}
 	fl4 = &inet->cork.fl.u.ip4;
 	rt = ip_route_connect(fl4, usin->sin_addr.s_addr, saddr, oif,

net/ipv4/ip_sockglue.c

@@ -1113,7 +1113,7 @@ int do_ip_setsockopt(struct sock *sk, int level, int optname,
 
 		ifindex = (__force int)ntohl((__force __be32)val);
 		if (ifindex == 0) {
-			inet->uc_index = 0;
+			WRITE_ONCE(inet->uc_index, 0);
 			err = 0;
 			break;
 		}
@@ -1130,7 +1130,7 @@ int do_ip_setsockopt(struct sock *sk, int level, int optname,
 		if (sk->sk_bound_dev_if && midx != sk->sk_bound_dev_if)
 			break;
 
-		inet->uc_index = ifindex;
+		WRITE_ONCE(inet->uc_index, ifindex);
 		err = 0;
 		break;
 	}
@@ -1633,6 +1633,9 @@ int do_ip_getsockopt(struct sock *sk, int level, int optname,
 			return -ENOTCONN;
 		goto copyval;
 	}
+	case IP_UNICAST_IF:
+		val = (__force int)htonl((__u32) READ_ONCE(inet->uc_index));
+		goto copyval;
 	}
 
 	if (needs_rtnl)
@@ -1640,9 +1643,6 @@ int do_ip_getsockopt(struct sock *sk, int level, int optname,
 	sockopt_lock_sock(sk);
 
 	switch (optname) {
-	case IP_UNICAST_IF:
-		val = (__force int)htonl((__u32) inet->uc_index);
-		break;
 	case IP_MULTICAST_IF:
 	{
 		struct in_addr addr;

net/ipv4/ping.c

@@ -777,7 +777,7 @@ static int ping_v4_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		if (!saddr)
 			saddr = inet->mc_addr;
 	} else if (!ipc.oif)
-		ipc.oif = inet->uc_index;
+		ipc.oif = READ_ONCE(inet->uc_index);
 
 	flowi4_init_output(&fl4, ipc.oif, ipc.sockc.mark, tos, scope,
 			   sk->sk_protocol, inet_sk_flowi_flags(sk), faddr,

net/ipv4/raw.c

@@ -482,7 +482,7 @@ static int raw_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	int free = 0;
 	__be32 daddr;
 	__be32 saddr;
-	int err;
+	int uc_index, err;
 	struct ip_options_data opt_copy;
 	struct raw_frag_vec rfv;
 	int hdrincl;
@@ -576,24 +576,25 @@ static int raw_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	tos = get_rttos(&ipc, inet);
 	scope = ip_sendmsg_scope(inet, &ipc, msg);
 
+	uc_index = READ_ONCE(inet->uc_index);
 	if (ipv4_is_multicast(daddr)) {
 		if (!ipc.oif || netif_index_is_l3_master(sock_net(sk), ipc.oif))
 			ipc.oif = inet->mc_index;
 		if (!saddr)
 			saddr = inet->mc_addr;
 	} else if (!ipc.oif) {
-		ipc.oif = inet->uc_index;
-	} else if (ipv4_is_lbcast(daddr) && inet->uc_index) {
+		ipc.oif = uc_index;
+	} else if (ipv4_is_lbcast(daddr) && uc_index) {
 		/* oif is set, packet is to local broadcast
 		 * and uc_index is set. oif is most likely set
 		 * by sk_bound_dev_if. If uc_index != oif check if the
 		 * oif is an L3 master and uc_index is an L3 slave.
 		 * If so, we want to allow the send using the uc_index.
 		 */
-		if (ipc.oif != inet->uc_index &&
+		if (ipc.oif != uc_index &&
 		    ipc.oif == l3mdev_master_ifindex_by_index(sock_net(sk),
-							      inet->uc_index)) {
-			ipc.oif = inet->uc_index;
+							      uc_index)) {
+			ipc.oif = uc_index;
 		}
 	}
 

net/ipv4/udp.c

@@ -1055,6 +1055,7 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	int (*getfrag)(void *, char *, int, int, int, struct sk_buff *);
 	struct sk_buff *skb;
 	struct ip_options_data opt_copy;
+	int uc_index;
 
 	if (len > 0xFFFF)
 		return -EMSGSIZE;
@@ -1173,6 +1174,7 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	if (scope == RT_SCOPE_LINK)
 		connected = 0;
 
+	uc_index = READ_ONCE(inet->uc_index);
 	if (ipv4_is_multicast(daddr)) {
 		if (!ipc.oif || netif_index_is_l3_master(sock_net(sk), ipc.oif))
 			ipc.oif = inet->mc_index;
@@ -1180,18 +1182,18 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 			saddr = inet->mc_addr;
 		connected = 0;
 	} else if (!ipc.oif) {
-		ipc.oif = inet->uc_index;
-	} else if (ipv4_is_lbcast(daddr) && inet->uc_index) {
+		ipc.oif = uc_index;
+	} else if (ipv4_is_lbcast(daddr) && uc_index) {
 		/* oif is set, packet is to local broadcast and
 		 * uc_index is set. oif is most likely set
 		 * by sk_bound_dev_if. If uc_index != oif check if the
 		 * oif is an L3 master and uc_index is an L3 slave.
 		 * If so, we want to allow the send using the uc_index.
 		 */
-		if (ipc.oif != inet->uc_index &&
+		if (ipc.oif != uc_index &&
 		    ipc.oif == l3mdev_master_ifindex_by_index(sock_net(sk),
-							      inet->uc_index)) {
-			ipc.oif = inet->uc_index;
+							      uc_index)) {
+			ipc.oif = uc_index;
 		}
 	}