netlink: annotate data races around dst_portid and dst_group

netlink_getname(), netlink_sendmsg() and netlink_getsockbyportid()
can read nlk->dst_portid and nlk->dst_group while another
thread is changing them.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/netlink/af_netlink.c

@@ -1099,8 +1099,9 @@ static int netlink_connect(struct socket *sock, struct sockaddr *addr,
 
 	if (addr->sa_family == AF_UNSPEC) {
 		sk->sk_state	= NETLINK_UNCONNECTED;
-		nlk->dst_portid	= 0;
-		nlk->dst_group  = 0;
+		/* dst_portid and dst_group can be read locklessly */
+		WRITE_ONCE(nlk->dst_portid, 0);
+		WRITE_ONCE(nlk->dst_group, 0);
 		return 0;
 	}
 	if (addr->sa_family != AF_NETLINK)
@@ -1122,8 +1123,9 @@ static int netlink_connect(struct socket *sock, struct sockaddr *addr,
 
 	if (err == 0) {
 		sk->sk_state	= NETLINK_CONNECTED;
-		nlk->dst_portid = nladdr->nl_pid;
-		nlk->dst_group  = ffs(nladdr->nl_groups);
+		/* dst_portid and dst_group can be read locklessly */
+		WRITE_ONCE(nlk->dst_portid, nladdr->nl_pid);
+		WRITE_ONCE(nlk->dst_group, ffs(nladdr->nl_groups));
 	}
 
 	return err;
@@ -1140,8 +1142,9 @@ static int netlink_getname(struct socket *sock, struct sockaddr *addr,
 	nladdr->nl_pad = 0;
 
 	if (peer) {
-		nladdr->nl_pid = nlk->dst_portid;
-		nladdr->nl_groups = netlink_group_mask(nlk->dst_group);
+		/* Paired with WRITE_ONCE() in netlink_connect() */
+		nladdr->nl_pid = READ_ONCE(nlk->dst_portid);
+		nladdr->nl_groups = netlink_group_mask(READ_ONCE(nlk->dst_group));
 	} else {
 		/* Paired with WRITE_ONCE() in netlink_insert() */
 		nladdr->nl_pid = READ_ONCE(nlk->portid);
@@ -1171,8 +1174,9 @@ static struct sock *netlink_getsockbyportid(struct sock *ssk, u32 portid)
 
 	/* Don't bother queuing skb if kernel socket has no input function */
 	nlk = nlk_sk(sock);
+	/* dst_portid can be changed in netlink_connect() */
 	if (sock->sk_state == NETLINK_CONNECTED &&
-	    nlk->dst_portid != nlk_sk(ssk)->portid) {
+	    READ_ONCE(nlk->dst_portid) != nlk_sk(ssk)->portid) {
 		sock_put(sock);
 		return ERR_PTR(-ECONNREFUSED);
 	}
@@ -1889,8 +1893,9 @@ static int netlink_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
 			goto out;
 		netlink_skb_flags |= NETLINK_SKB_DST;
 	} else {
-		dst_portid = nlk->dst_portid;
-		dst_group = nlk->dst_group;
+		/* Paired with WRITE_ONCE() in netlink_connect() */
+		dst_portid = READ_ONCE(nlk->dst_portid);
+		dst_group = READ_ONCE(nlk->dst_group);
 	}
 
 	/* Paired with WRITE_ONCE() in netlink_insert() */