l2tp: Refactor the codes with existing macros instead of literal number

BugLink: https://bugs.launchpad.net/bugs/1874045

commit 54c151d9 upstream.

Use PPP_ALLSTATIONS, PPP_UI, and SEND_SHUTDOWN instead of 0xff,
0x03, and 2 separately.
Signed-off-by: Gao Feng <fgao@ikuai8.com>
Acked-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>

net/l2tp/l2tp_ppp.c

@@ -177,7 +177,7 @@ static int pppol2tp_recv_payload_hook(struct sk_buff *skb)
 	if (!pskb_may_pull(skb, 2))
 		return 1;
 
-	if ((skb->data[0] == 0xff) && (skb->data[1] == 0x03))
+	if ((skb->data[0] == PPP_ALLSTATIONS) && (skb->data[1] == PPP_UI))
 		skb_pull(skb, 2);
 
 	return 0;
@@ -297,7 +297,6 @@ static void pppol2tp_session_sock_put(struct l2tp_session *session)
 static int pppol2tp_sendmsg(struct socket *sock, struct msghdr *m,
 			    size_t total_len)
 {
-	static const unsigned char ppph[2] = { 0xff, 0x03 };
 	struct sock *sk = sock->sk;
 	struct sk_buff *skb;
 	int error;
@@ -327,7 +326,7 @@ static int pppol2tp_sendmsg(struct socket *sock, struct msghdr *m,
 	error = -ENOMEM;
 	skb = sock_wmalloc(sk, NET_SKB_PAD + sizeof(struct iphdr) +
 			   uhlen + session->hdr_len +
-			   sizeof(ppph) + total_len,
+			   2 + total_len, /* 2 bytes for PPP_ALLSTATIONS & PPP_UI */
 			   0, GFP_KERNEL);
 	if (!skb)
 		goto error_put_sess_tun;
@@ -340,8 +339,8 @@ static int pppol2tp_sendmsg(struct socket *sock, struct msghdr *m,
 	skb_reserve(skb, uhlen);
 
 	/* Add PPP header */
-	skb->data[0] = ppph[0];
-	skb->data[1] = ppph[1];
+	skb->data[0] = PPP_ALLSTATIONS;
+	skb->data[1] = PPP_UI;
 	skb_put(skb, 2);
 
 	/* Copy user data into skb */
@@ -384,7 +383,6 @@ static int pppol2tp_sendmsg(struct socket *sock, struct msghdr *m,
  */
 static int pppol2tp_xmit(struct ppp_channel *chan, struct sk_buff *skb)
 {
-	static const u8 ppph[2] = { 0xff, 0x03 };
 	struct sock *sk = (struct sock *) chan->private;
 	struct sock *sk_tun;
 	struct l2tp_session *session;
@@ -413,14 +411,14 @@ static int pppol2tp_xmit(struct ppp_channel *chan, struct sk_buff *skb)
 		   sizeof(struct iphdr) + /* IP header */
 		   uhlen +		/* UDP header (if L2TP_ENCAPTYPE_UDP) */
 		   session->hdr_len +	/* L2TP header */
-		   sizeof(ppph);	/* PPP header */
+		   2;			/* 2 bytes for PPP_ALLSTATIONS & PPP_UI */
 	if (skb_cow_head(skb, headroom))
 		goto abort_put_sess_tun;
 
 	/* Setup PPP header */
-	__skb_push(skb, sizeof(ppph));
-	skb->data[0] = ppph[0];
-	skb->data[1] = ppph[1];
+	__skb_push(skb, 2);
+	skb->data[0] = PPP_ALLSTATIONS;
+	skb->data[1] = PPP_UI;
 
 	local_bh_disable();
 	l2tp_xmit_skb(session, skb, session->hdr_len);
@@ -455,7 +453,7 @@ static void pppol2tp_session_close(struct l2tp_session *session)
 	BUG_ON(session->magic != L2TP_SESSION_MAGIC);
 
 	if (sock) {
-		inet_shutdown(sock, 2);
+		inet_shutdown(sock, SEND_SHUTDOWN);
 		/* Don't let the session go away before our socket does */
 		l2tp_session_inc_refcount(session);
 	}