Merge branch 'l2tp-fixes'

Guillaume Nault says:

====================
l2tp: pppol2tp_connect() fixes

This series fixes a few remaining issues with pppol2tp_connect().

It doesn't try to prevent invalid configurations that have no effect on
kernel's reliability. That would be work for a future patch set.

Patch 2 is the most important as it avoids an invalid pointer
dereference crashing the kernel. It depends on patch 1 for correctly
identifying L2TP session types.

Patches 3 and 4 avoid creating stale tunnels and sessions.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

net/l2tp/l2tp_ppp.c

@@ -612,6 +612,8 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
 	u32 session_id, peer_session_id;
 	bool drop_refcnt = false;
 	bool drop_tunnel = false;
+	bool new_session = false;
+	bool new_tunnel = false;
 	int ver = 2;
 	int fd;
 
@@ -701,6 +703,15 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
 				.encap = L2TP_ENCAPTYPE_UDP,
 				.debug = 0,
 			};
+
+			/* Prevent l2tp_tunnel_register() from trying to set up
+			 * a kernel socket.
+			 */
+			if (fd < 0) {
+				error = -EBADF;
+				goto end;
+			}
+
 			error = l2tp_tunnel_create(sock_net(sk), fd, ver, tunnel_id, peer_tunnel_id, &tcfg, &tunnel);
 			if (error < 0)
 				goto end;
@@ -713,6 +724,7 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
 				goto end;
 			}
 			drop_tunnel = true;
+			new_tunnel = true;
 		}
 	} else {
 		/* Error if we can't find the tunnel */
@@ -734,6 +746,12 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
 	session = l2tp_session_get(sock_net(sk), tunnel, session_id);
 	if (session) {
 		drop_refcnt = true;
+
+		if (session->pwtype != L2TP_PWTYPE_PPP) {
+			error = -EPROTOTYPE;
+			goto end;
+		}
+
 		ps = l2tp_session_priv(session);
 
 		/* Using a pre-existing session is fine as long as it hasn't
@@ -751,6 +769,7 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
 		/* Default MTU must allow space for UDP/L2TP/PPP headers */
 		cfg.mtu = 1500 - PPPOL2TP_HEADER_OVERHEAD;
 		cfg.mru = cfg.mtu;
+		cfg.pw_type = L2TP_PWTYPE_PPP;
 
 		session = l2tp_session_create(sizeof(struct pppol2tp_session),
 					      tunnel, session_id,
@@ -772,6 +791,7 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
 			goto end;
 		}
 		drop_refcnt = true;
+		new_session = true;
 	}
 
 	/* Special case: if source & dest session_id == 0x0000, this
@@ -818,6 +838,12 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
 		  session->name);
 
 end:
+	if (error) {
+		if (new_session)
+			l2tp_session_delete(session);
+		if (new_tunnel)
+			l2tp_tunnel_delete(tunnel);
+	}
 	if (drop_refcnt)
 		l2tp_session_dec_refcount(session);
 	if (drop_tunnel)