net: udp: annotate data race around udp_sk(sk)->corkflag

up->corkflag field can be read or written without any lock.
Annotate accesses to avoid possible syzbot/KCSAN reports.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/udp.c

@@ -1053,7 +1053,7 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	__be16 dport;
 	u8  tos;
 	int err, is_udplite = IS_UDPLITE(sk);
-	int corkreq = up->corkflag || msg->msg_flags&MSG_MORE;
+	int corkreq = READ_ONCE(up->corkflag) || msg->msg_flags&MSG_MORE;
 	int (*getfrag)(void *, char *, int, int, int, struct sk_buff *);
 	struct sk_buff *skb;
 	struct ip_options_data opt_copy;
@@ -1361,7 +1361,7 @@ int udp_sendpage(struct sock *sk, struct page *page, int offset,
 	}
 
 	up->len += size;
-	if (!(up->corkflag || (flags&MSG_MORE)))
+	if (!(READ_ONCE(up->corkflag) || (flags&MSG_MORE)))
 		ret = udp_push_pending_frames(sk);
 	if (!ret)
 		ret = size;
@@ -2662,9 +2662,9 @@ int udp_lib_setsockopt(struct sock *sk, int level, int optname,
 	switch (optname) {
 	case UDP_CORK:
 		if (val != 0) {
-			up->corkflag = 1;
+			WRITE_ONCE(up->corkflag, 1);
 		} else {
-			up->corkflag = 0;
+			WRITE_ONCE(up->corkflag, 0);
 			lock_sock(sk);
 			push_pending_frames(sk);
 			release_sock(sk);
@@ -2787,7 +2787,7 @@ int udp_lib_getsockopt(struct sock *sk, int level, int optname,
 
 	switch (optname) {
 	case UDP_CORK:
-		val = up->corkflag;
+		val = READ_ONCE(up->corkflag);
 		break;
 
 	case UDP_ENCAP:

net/ipv6/udp.c

@@ -1303,7 +1303,7 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	int addr_len = msg->msg_namelen;
 	bool connected = false;
 	int ulen = len;
-	int corkreq = up->corkflag || msg->msg_flags&MSG_MORE;
+	int corkreq = READ_ONCE(up->corkflag) || msg->msg_flags&MSG_MORE;
 	int err;
 	int is_udplite = IS_UDPLITE(sk);
 	int (*getfrag)(void *, char *, int, int, int, struct sk_buff *);