l2tp: Add netlink control API for L2TP

In L2TPv3, we need to create/delete/modify/query L2TP tunnel and
session contexts. The number of parameters is significant. So let's
use netlink. Userspace uses this API to control L2TP tunnel/session
contexts in the kernel.

The previous pppol2tp driver was managed using [gs]etsockopt(). This
API is retained for backwards compatibility. Unlike L2TPv2 which
carries only PPP frames, L2TPv3 can carry raw ethernet frames or other
frame types and these do not always have an associated socket
family. Therefore, we need a way to use L2TP sessions that doesn't
require a socket type for each supported frame type. Hence netlink is
used.

Signed-off-by: James Chapman <jchapman@katalix.com>
Reviewed-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 139 insertions, 23 deletions

diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index 63fc62baeeb9..d64f081f2b1c 100644
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -87,6 +87,7 @@
 #include <linux/hash.h>
 #include <linux/sort.h>
 #include <linux/proc_fs.h>
+#include <linux/l2tp.h>
 #include <linux/nsproxy.h>
 #include <net/net_namespace.h>
 #include <net/netns/generic.h>
@@ -656,17 +657,23 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
         if (tunnel_id == 0)
                 goto end;
 
+        tunnel = l2tp_tunnel_find(sock_net(sk), tunnel_id);
+
         /* Special case: create tunnel context if session_id and
          * peer_session_id is 0. Otherwise look up tunnel using supplied
          * tunnel id.
          */
         if ((session_id == 0) && (peer_session_id == 0)) {
-                error = l2tp_tunnel_create(sock_net(sk), fd, ver, tunnel_id, peer_tunnel_id, NULL, &tunnel);
-                if (error < 0)
-                        goto end;
+                if (tunnel == NULL) {
+                        struct l2tp_tunnel_cfg tcfg = {
+                                .encap = L2TP_ENCAPTYPE_UDP,
+                                .debug = 0,
+                        };
+                        error = l2tp_tunnel_create(sock_net(sk), fd, ver, tunnel_id, peer_tunnel_id, &tcfg, &tunnel);
+                        if (error < 0)
+                                goto end;
+                }
         } else {
-                tunnel = l2tp_tunnel_find(sock_net(sk), tunnel_id);
-
                 /* Error if we can't find the tunnel */
                 error = -ENOENT;
                 if (tunnel == NULL)
@@ -680,28 +687,46 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
         if (tunnel->recv_payload_hook == NULL)
                 tunnel->recv_payload_hook = pppol2tp_recv_payload_hook;
 
-        /* Check that this session doesn't already exist */
-        error = -EEXIST;
-        session = l2tp_session_find(sock_net(sk), tunnel, session_id);
-        if (session != NULL)
-                goto end;
-
-        /* Default MTU values. */
-        if (cfg.mtu == 0)
-                cfg.mtu = 1500 - PPPOL2TP_HEADER_OVERHEAD;
-        if (cfg.mru == 0)
-                cfg.mru = cfg.mtu;
-        cfg.debug = tunnel->debug;
+        if (tunnel->peer_tunnel_id == 0) {
+                if (ver == 2)
+                        tunnel->peer_tunnel_id = sp->pppol2tp.d_tunnel;
+                else
+                        tunnel->peer_tunnel_id = sp3->pppol2tp.d_tunnel;
+        }
 
-        /* Allocate and initialize a new session context. */
-        session = l2tp_session_create(sizeof(struct pppol2tp_session),
-                                      tunnel, session_id,
-                                      peer_session_id, &cfg);
+        /* Create session if it doesn't already exist. We handle the
+         * case where a session was previously created by the netlink
+         * interface by checking that the session doesn't already have
+         * a socket and its tunnel socket are what we expect. If any
+         * of those checks fail, return EEXIST to the caller.
+         */
+        session = l2tp_session_find(sock_net(sk), tunnel, session_id);
         if (session == NULL) {
-                error = -ENOMEM;
-                goto end;
+                /* Default MTU must allow space for UDP/L2TP/PPP
+                 * headers.
+                 */
+                cfg.mtu = cfg.mru = 1500 - PPPOL2TP_HEADER_OVERHEAD;
+
+                /* Allocate and initialize a new session context. */
+                session = l2tp_session_create(sizeof(struct pppol2tp_session),
+                                              tunnel, session_id,
+                                              peer_session_id, &cfg);
+                if (session == NULL) {
+                        error = -ENOMEM;
+                        goto end;
+                }
+        } else {
+                ps = l2tp_session_priv(session);
+                error = -EEXIST;
+                if (ps->sock != NULL)
+                        goto end;
+
+                /* consistency checks */
+                if (ps->tunnel_sock != tunnel->sock)
+                        goto end;
         }
 
+        /* Associate session with its PPPoL2TP socket */
         ps = l2tp_session_priv(session);
         ps->owner            = current->pid;
         ps->sock             = sk;
@@ -764,6 +789,74 @@ end:
         return error;
 }
 
+#ifdef CONFIG_L2TP_V3
+
+/* Called when creating sessions via the netlink interface.
+ */
+static int pppol2tp_session_create(struct net *net, u32 tunnel_id, u32 session_id, u32 peer_session_id, struct l2tp_session_cfg *cfg)
+{
+        int error;
+        struct l2tp_tunnel *tunnel;
+        struct l2tp_session *session;
+        struct pppol2tp_session *ps;
+
+        tunnel = l2tp_tunnel_find(net, tunnel_id);
+
+        /* Error if we can't find the tunnel */
+        error = -ENOENT;
+        if (tunnel == NULL)
+                goto out;
+
+        /* Error if tunnel socket is not prepped */
+        if (tunnel->sock == NULL)
+                goto out;
+
+        /* Check that this session doesn't already exist */
+        error = -EEXIST;
+        session = l2tp_session_find(net, tunnel, session_id);
+        if (session != NULL)
+                goto out;
+
+        /* Default MTU values. */
+        if (cfg->mtu == 0)
+                cfg->mtu = 1500 - PPPOL2TP_HEADER_OVERHEAD;
+        if (cfg->mru == 0)
+                cfg->mru = cfg->mtu;
+
+        /* Allocate and initialize a new session context. */
+        error = -ENOMEM;
+        session = l2tp_session_create(sizeof(struct pppol2tp_session),
+                                      tunnel, session_id,
+                                      peer_session_id, cfg);
+        if (session == NULL)
+                goto out;
+
+        ps = l2tp_session_priv(session);
+        ps->tunnel_sock = tunnel->sock;
+
+        PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
+               "%s: created\n", session->name);
+
+        error = 0;
+
+out:
+        return error;
+}
+
+/* Called when deleting sessions via the netlink interface.
+ */
+static int pppol2tp_session_delete(struct l2tp_session *session)
+{
+        struct pppol2tp_session *ps = l2tp_session_priv(session);
+
+        if (ps->sock == NULL)
+                l2tp_session_dec_refcount(session);
+
+        return 0;
+}
+
+#endif /* CONFIG_L2TP_V3 */
+
 /* getname() support.
  */
 static int pppol2tp_getname(struct socket *sock, struct sockaddr *uaddr,
@@ -1660,6 +1753,15 @@ static struct pppox_proto pppol2tp_proto = {
         .ioctl          = pppol2tp_ioctl
 };
 
+#ifdef CONFIG_L2TP_V3
+
+static const struct l2tp_nl_cmd_ops pppol2tp_nl_cmd_ops = {
+        .session_create = pppol2tp_session_create,
+        .session_delete = pppol2tp_session_delete,
+};
+
+#endif /* CONFIG_L2TP_V3 */
+
 static int __init pppol2tp_init(void)
 {
         int err;
@@ -1676,11 +1778,22 @@ static int __init pppol2tp_init(void)
         if (err)
                 goto out_unregister_pppol2tp_proto;
 
+#ifdef CONFIG_L2TP_V3
+        err = l2tp_nl_register_ops(L2TP_PWTYPE_PPP, &pppol2tp_nl_cmd_ops);
+        if (err)
+                goto out_unregister_pppox;
+#endif
+
         printk(KERN_INFO "PPPoL2TP kernel driver, %s\n",
                PPPOL2TP_DRV_VERSION);
 
 out:
         return err;
+
+#ifdef CONFIG_L2TP_V3
+out_unregister_pppox:
+        unregister_pppox_proto(PX_PROTO_OL2TP);
+#endif
 out_unregister_pppol2tp_proto:
         proto_unregister(&pppol2tp_sk_proto);
 out_unregister_pppol2tp_pernet:
@@ -1690,6 +1803,9 @@ out_unregister_pppol2tp_pernet:
 
 static void __exit pppol2tp_exit(void)
 {
+#ifdef CONFIG_L2TP_V3
+        l2tp_nl_unregister_ops(L2TP_PWTYPE_PPP);
+#endif
         unregister_pppox_proto(PX_PROTO_OL2TP);
         proto_unregister(&pppol2tp_sk_proto);
         unregister_pernet_device(&pppol2tp_net_ops);