l2tp: Add L2TPv3 IP encapsulation (no UDP) support

This patch adds a new L2TPIP socket family and modifies the core to
handle the case where there is no UDP header in the L2TP
packet. L2TP/IP uses IP protocol 115. Since L2TP/UDP and L2TP/IP
packets differ in layout, the datapath packet handling code needs
changes too. Userspace uses an L2TPIP socket instead of a UDP socket
when IP encapsulation is required.

We can't use raw sockets for this because the semantics of raw sockets
don't lend themselves to the socket-per-tunnel model - we need to

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 103 insertions, 60 deletions

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 0eee1a65f1b1..1739d04367e4 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -36,8 +36,10 @@
 #include <linux/inetdevice.h>
 #include <linux/skbuff.h>
 #include <linux/init.h>
+#include <linux/in.h>
 #include <linux/ip.h>
 #include <linux/udp.h>
+#include <linux/l2tp.h>
 #include <linux/hash.h>
 #include <linux/sort.h>
 #include <linux/file.h>
@@ -48,6 +50,7 @@
 #include <net/ip.h>
 #include <net/udp.h>
 #include <net/xfrm.h>
+#include <net/protocol.h>
 
 #include <asm/byteorder.h>
 #include <asm/atomic.h>
@@ -849,15 +852,21 @@ static int l2tp_build_l2tpv2_header(struct l2tp_session *session, void *buf)
 
 static int l2tp_build_l2tpv3_header(struct l2tp_session *session, void *buf)
 {
+        struct l2tp_tunnel *tunnel = session->tunnel;
         char *bufp = buf;
         char *optr = bufp;
-        u16 flags = L2TP_HDR_VER_3;
 
-        /* Setup L2TP header. */
-        *((__be16 *) bufp) = htons(flags);
-        bufp += 2;
-        *((__be16 *) bufp) = 0;
-        bufp += 2;
+        /* Setup L2TP header. The header differs slightly for UDP and
+         * IP encapsulations. For UDP, there is 4 bytes of flags.
+         */
+        if (tunnel->encap == L2TP_ENCAPTYPE_UDP) {
+                u16 flags = L2TP_HDR_VER_3;
+                *((__be16 *) bufp) = htons(flags);
+                bufp += 2;
+                *((__be16 *) bufp) = 0;
+                bufp += 2;
+        }
+
         *((__be32 *) bufp) = htonl(session->peer_session_id);
         bufp += 4;
         if (session->cookie_len) {
@@ -902,10 +911,11 @@ int l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb, size_t dat
 
         if (session->debug & L2TP_MSG_DATA) {
                 int i;
-                unsigned char *datap = skb->data + sizeof(struct udphdr);
+                int uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(struct udphdr) : 0;
+                unsigned char *datap = skb->data + uhlen;
 
                 printk(KERN_DEBUG "%s: xmit:", session->name);
-                for (i = 0; i < (len - sizeof(struct udphdr)); i++) {
+                for (i = 0; i < (len - uhlen); i++) {
                         printk(" %02X", *datap++);
                         if (i == 31) {
                                 printk(" ...");
@@ -956,21 +966,23 @@ static inline void l2tp_skb_set_owner_w(struct sk_buff *skb, struct sock *sk)
 int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb, int hdr_len)
 {
         int data_len = skb->len;
-        struct sock *sk = session->tunnel->sock;
+        struct l2tp_tunnel *tunnel = session->tunnel;
+        struct sock *sk = tunnel->sock;
         struct udphdr *uh;
-        unsigned int udp_len;
         struct inet_sock *inet;
         __wsum csum;
         int old_headroom;
         int new_headroom;
         int headroom;
+        int uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(struct udphdr) : 0;
+        int udp_len;
 
         /* Check that there's enough headroom in the skb to insert IP,
          * UDP and L2TP headers. If not enough, expand it to
          * make room. Adjust truesize.
          */
         headroom = NET_SKB_PAD + sizeof(struct iphdr) +
-                sizeof(struct udphdr) + hdr_len;
+                uhlen + hdr_len;
         old_headroom = skb_headroom(skb);
         if (skb_cow_head(skb, headroom))
                 goto abort;
@@ -981,18 +993,8 @@ int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb, int hdr_len
 
         /* Setup L2TP header */
         session->build_header(session, __skb_push(skb, hdr_len));
-        udp_len = sizeof(struct udphdr) + hdr_len + data_len;
-
-        /* Setup UDP header */
-        inet = inet_sk(sk);
-        __skb_push(skb, sizeof(*uh));
-        skb_reset_transport_header(skb);
-        uh = udp_hdr(skb);
-        uh->source = inet->inet_sport;
-        uh->dest = inet->inet_dport;
-        uh->len = htons(udp_len);
-        uh->check = 0;
 
+        /* Reset skb netfilter state */
         memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
         IPCB(skb)->flags &= ~(IPSKB_XFRM_TUNNEL_SIZE | IPSKB_XFRM_TRANSFORMED |
                               IPSKB_REROUTED);
@@ -1001,29 +1003,48 @@ int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb, int hdr_len
         /* Get routing info from the tunnel socket */
         skb_dst_drop(skb);
         skb_dst_set(skb, dst_clone(__sk_dst_get(sk)));
-        l2tp_skb_set_owner_w(skb, sk);
 
-        /* Calculate UDP checksum if configured to do so */
-        if (sk->sk_no_check == UDP_CSUM_NOXMIT)
-                skb->ip_summed = CHECKSUM_NONE;
-        else if ((skb_dst(skb) && skb_dst(skb)->dev) &&
-                 (!(skb_dst(skb)->dev->features & NETIF_F_V4_CSUM))) {
-                skb->ip_summed = CHECKSUM_COMPLETE;
-                csum = skb_checksum(skb, 0, udp_len, 0);
-                uh->check = csum_tcpudp_magic(inet->inet_saddr,
-                                              inet->inet_daddr,
-                                              udp_len, IPPROTO_UDP, csum);
-                if (uh->check == 0)
-                        uh->check = CSUM_MANGLED_0;
-        } else {
-                skb->ip_summed = CHECKSUM_PARTIAL;
-                skb->csum_start = skb_transport_header(skb) - skb->head;
-                skb->csum_offset = offsetof(struct udphdr, check);
-                uh->check = ~csum_tcpudp_magic(inet->inet_saddr,
-                                               inet->inet_daddr,
-                                               udp_len, IPPROTO_UDP, 0);
+        switch (tunnel->encap) {
+        case L2TP_ENCAPTYPE_UDP:
+                /* Setup UDP header */
+                inet = inet_sk(sk);
+                __skb_push(skb, sizeof(*uh));
+                skb_reset_transport_header(skb);
+                uh = udp_hdr(skb);
+                uh->source = inet->inet_sport;
+                uh->dest = inet->inet_dport;
+                udp_len = uhlen + hdr_len + data_len;
+                uh->len = htons(udp_len);
+                uh->check = 0;
+
+                /* Calculate UDP checksum if configured to do so */
+                if (sk->sk_no_check == UDP_CSUM_NOXMIT)
+                        skb->ip_summed = CHECKSUM_NONE;
+                else if ((skb_dst(skb) && skb_dst(skb)->dev) &&
+                         (!(skb_dst(skb)->dev->features & NETIF_F_V4_CSUM))) {
+                        skb->ip_summed = CHECKSUM_COMPLETE;
+                        csum = skb_checksum(skb, 0, udp_len, 0);
+                        uh->check = csum_tcpudp_magic(inet->inet_saddr,
+                                                      inet->inet_daddr,
+                                                      udp_len, IPPROTO_UDP, csum);
+                        if (uh->check == 0)
+                                uh->check = CSUM_MANGLED_0;
+                } else {
+                        skb->ip_summed = CHECKSUM_PARTIAL;
+                        skb->csum_start = skb_transport_header(skb) - skb->head;
+                        skb->csum_offset = offsetof(struct udphdr, check);
+                        uh->check = ~csum_tcpudp_magic(inet->inet_saddr,
+                                                       inet->inet_daddr,
+                                                       udp_len, IPPROTO_UDP, 0);
+                }
+                break;
+
+        case L2TP_ENCAPTYPE_IP:
+                break;
         }
 
+        l2tp_skb_set_owner_w(skb, sk);
+
         l2tp_xmit_core(session, skb, data_len);
 
 abort:
@@ -1053,9 +1074,15 @@ void l2tp_tunnel_destruct(struct sock *sk)
         /* Close all sessions */
         l2tp_tunnel_closeall(tunnel);
 
-        /* No longer an encapsulation socket. See net/ipv4/udp.c */
-        (udp_sk(sk))->encap_type = 0;
-        (udp_sk(sk))->encap_rcv = NULL;
+        switch (tunnel->encap) {
+        case L2TP_ENCAPTYPE_UDP:
+                /* No longer an encapsulation socket. See net/ipv4/udp.c */
+                (udp_sk(sk))->encap_type = 0;
+                (udp_sk(sk))->encap_rcv = NULL;
+                break;
+        case L2TP_ENCAPTYPE_IP:
+                break;
+        }
 
         /* Remove hooks into tunnel socket */
         tunnel->sock = NULL;
@@ -1168,6 +1195,7 @@ int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id, u32
         struct socket *sock = NULL;
         struct sock *sk = NULL;
         struct l2tp_net *pn;
+        enum l2tp_encap_type encap = L2TP_ENCAPTYPE_UDP;
 
         /* Get the tunnel socket from the fd, which was opened by
          * the userspace L2TP daemon.
@@ -1182,18 +1210,27 @@ int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id, u32
 
         sk = sock->sk;
 
+        if (cfg != NULL)
+                encap = cfg->encap;
+
         /* Quick sanity checks */
-        err = -EPROTONOSUPPORT;
-        if (sk->sk_protocol != IPPROTO_UDP) {
-                printk(KERN_ERR "tunl %hu: fd %d wrong protocol, got %d, expected %d\n",
-                       tunnel_id, fd, sk->sk_protocol, IPPROTO_UDP);
-                goto err;
-        }
-        err = -EAFNOSUPPORT;
-        if (sock->ops->family != AF_INET) {
-                printk(KERN_ERR "tunl %hu: fd %d wrong family, got %d, expected %d\n",
-                       tunnel_id, fd, sock->ops->family, AF_INET);
-                goto err;
+        switch (encap) {
+        case L2TP_ENCAPTYPE_UDP:
+                err = -EPROTONOSUPPORT;
+                if (sk->sk_protocol != IPPROTO_UDP) {
+                        printk(KERN_ERR "tunl %hu: fd %d wrong protocol, got %d, expected %d\n",
+                               tunnel_id, fd, sk->sk_protocol, IPPROTO_UDP);
+                        goto err;
+                }
+                break;
+        case L2TP_ENCAPTYPE_IP:
+                err = -EPROTONOSUPPORT;
+                if (sk->sk_protocol != IPPROTO_L2TP) {
+                        printk(KERN_ERR "tunl %hu: fd %d wrong protocol, got %d, expected %d\n",
+                               tunnel_id, fd, sk->sk_protocol, IPPROTO_L2TP);
+                        goto err;
+                }
+                break;
         }
 
         /* Check if this socket has already been prepped */
@@ -1223,12 +1260,16 @@ int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id, u32
         tunnel->l2tp_net = net;
         pn = l2tp_pernet(net);
 
-        if (cfg)
+        if (cfg != NULL)
                 tunnel->debug = cfg->debug;
 
         /* Mark socket as an encapsulation socket. See net/ipv4/udp.c */
-        udp_sk(sk)->encap_type = UDP_ENCAP_L2TPINUDP;
-        udp_sk(sk)->encap_rcv = l2tp_udp_encap_recv;
+        tunnel->encap = encap;
+        if (encap == L2TP_ENCAPTYPE_UDP) {
+                /* Mark socket as an encapsulation socket. See net/ipv4/udp.c */
+                udp_sk(sk)->encap_type = UDP_ENCAP_L2TPINUDP;
+                udp_sk(sk)->encap_rcv = l2tp_udp_encap_recv;
+        }
 
         sk->sk_user_data = tunnel;
 
@@ -1318,7 +1359,9 @@ void l2tp_session_set_header_len(struct l2tp_session *session, int version)
                 if (session->send_seq)
                         session->hdr_len += 4;
         } else {
-                session->hdr_len = 8 + session->cookie_len + session->l2specific_len + session->offset;
+                session->hdr_len = 4 + session->cookie_len + session->l2specific_len + session->offset;
+                if (session->tunnel->encap == L2TP_ENCAPTYPE_UDP)
+                        session->hdr_len += 4;
         }
 
 }