tun: free skb in early errors

tun_recvmsg() supports accepting skb by msg_control after
commit ac77cfd4 ("tun: support receiving skb through msg_control"),
the skb if presented should be freed no matter how far it can go
along, otherwise it would be leaked.

This patch fixes several missed cases.
Signed-off-by: Wei Xu <wexu@redhat.com>
Reported-by: Matthew Rosato <mjrosato@linux.vnet.ibm.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -1952,8 +1952,11 @@ static ssize_t tun_do_read(struct tun_struct *tun, struct tun_file *tfile,
 
 	tun_debug(KERN_INFO, tun, "tun_do_read\n");
 
-	if (!iov_iter_count(to))
+	if (!iov_iter_count(to)) {
+		if (skb)
+			kfree_skb(skb);
 		return 0;
+	}
 
 	if (!skb) {
 		/* Read frames from ring */
@@ -2069,22 +2072,24 @@ static int tun_recvmsg(struct socket *sock, struct msghdr *m, size_t total_len,
 {
 	struct tun_file *tfile = container_of(sock, struct tun_file, socket);
 	struct tun_struct *tun = tun_get(tfile);
+	struct sk_buff *skb = m->msg_control;
 	int ret;
 
-	if (!tun)
-		return -EBADFD;
+	if (!tun) {
+		ret = -EBADFD;
+		goto out_free_skb;
+	}
 
 	if (flags & ~(MSG_DONTWAIT|MSG_TRUNC|MSG_ERRQUEUE)) {
 		ret = -EINVAL;
-		goto out;
+		goto out_put_tun;
 	}
 	if (flags & MSG_ERRQUEUE) {
 		ret = sock_recv_errqueue(sock->sk, m, total_len,
 					 SOL_PACKET, TUN_TX_TIMESTAMP);
 		goto out;
 	}
-	ret = tun_do_read(tun, tfile, &m->msg_iter, flags & MSG_DONTWAIT,
-			  m->msg_control);
+	ret = tun_do_read(tun, tfile, &m->msg_iter, flags & MSG_DONTWAIT, skb);
 	if (ret > (ssize_t)total_len) {
 		m->msg_flags |= MSG_TRUNC;
 		ret = flags & MSG_TRUNC ? ret : total_len;
@@ -2092,6 +2097,13 @@ static int tun_recvmsg(struct socket *sock, struct msghdr *m, size_t total_len,
 out:
 	tun_put(tun);
 	return ret;
+
+out_put_tun:
+	tun_put(tun);
+out_free_skb:
+	if (skb)
+		kfree_skb(skb);
+	return ret;
 }
 
 static int tun_peek_len(struct socket *sock)