l2tp: ignore L2TP_ATTR_MTU

This attribute's handling is broken. It can only be used when creating
Ethernet pseudo-wires, in which case its value can be used as the
initial MTU for the l2tpeth device.
However, when handling update requests, L2TP_ATTR_MTU only modifies
session->mtu. This value is never propagated to the l2tpeth device.
Dump requests also return the value of session->mtu, which is not
synchronised anymore with the device MTU.

The same problem occurs if the device MTU is properly updated using the
generic IFLA_MTU attribute. In this case, session->mtu is not updated,
and L2TP_ATTR_MTU will report an invalid value again when dumping the
session.

It does not seem worthwhile to complexify l2tp_eth.c to synchronise
session->mtu with the device MTU. Even the ip-l2tp manpage advises to
use 'ip link' to initialise the MTU of l2tpeth devices (iproute2 does
not handle L2TP_ATTR_MTU at all anyway). So let's just ignore it
entirely.

Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/uapi/linux/l2tp.h b/include/uapi/linux/l2tp.h
index 8bb8c7c..61158f5 100644 (file)
--- a/include/uapi/linux/l2tp.h
+++ b/include/uapi/linux/l2tp.h
@@ -119,7 +119,7 @@ enum {
        L2TP_ATTR_IP_DADDR,             /* u32 */
        L2TP_ATTR_UDP_SPORT,            /* u16 */
        L2TP_ATTR_UDP_DPORT,            /* u16 */
-       L2TP_ATTR_MTU,                  /* u16 */
+       L2TP_ATTR_MTU,                  /* u16 (not used) */
        L2TP_ATTR_MRU,                  /* u16 (not used) */
        L2TP_ATTR_STATS,                /* nested */
        L2TP_ATTR_IP6_SADDR,            /* struct in6_addr */

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index c61a467..ac6a00b 100644 (file)
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1674,7 +1674,6 @@ struct l2tp_session *l2tp_session_create(int priv_size, struct l2tp_tunnel *tunn
                if (cfg) {
                        session->pwtype = cfg->pw_type;
                        session->debug = cfg->debug;
-                       session->mtu = cfg->mtu;
                        session->send_seq = cfg->send_seq;
                        session->recv_seq = cfg->recv_seq;
                        session->lns_mode = cfg->lns_mode;

diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index 1ca3962..5804065 100644 (file)
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -64,7 +64,6 @@ struct l2tp_session_cfg {
        int                     peer_cookie_len; /* 0, 4 or 8 bytes */
        int                     reorder_timeout; /* configured reorder timeout
                                                  * (in jiffies) */
-       int                     mtu;
        char                    *ifname;
 };
 
@@ -108,7 +107,6 @@ struct l2tp_session {
        int                     reorder_timeout; /* configured reorder timeout
                                                  * (in jiffies) */
        int                     reorder_skip;   /* set if skip to next nr */
-       int                     mtu;
        enum l2tp_pwtype        pwtype;
        struct l2tp_stats       stats;
        struct hlist_node       global_hlist;   /* Global hash list node */

diff --git a/net/l2tp/l2tp_debugfs.c b/net/l2tp/l2tp_debugfs.c
index aee2717..9821a14 100644 (file)
--- a/net/l2tp/l2tp_debugfs.c
+++ b/net/l2tp/l2tp_debugfs.c
@@ -191,8 +191,7 @@ static void l2tp_dfs_seq_session_show(struct seq_file *m, void *v)
        if (session->send_seq || session->recv_seq)
                seq_printf(m, "   nr %hu, ns %hu\n", session->nr, session->ns);
        seq_printf(m, "   refcnt %d\n", refcount_read(&session->ref_count));
-       seq_printf(m, "   config %d/0/%c/%c/-/%s %08x %u\n",
-                  session->mtu,
+       seq_printf(m, "   config 0/0/%c/%c/-/%s %08x %u\n",
                   session->recv_seq ? 'R' : '-',
                   session->send_seq ? 'S' : '-',
                   session->lns_mode ? "LNS" : "LAC",

diff --git a/net/l2tp/l2tp_eth.c b/net/l2tp/l2tp_eth.c
index cfca5e6..3728986 100644 (file)
--- a/net/l2tp/l2tp_eth.c
+++ b/net/l2tp/l2tp_eth.c
@@ -234,14 +234,11 @@ static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tunnel,
                overhead += sizeof(struct udphdr);
                dev->needed_headroom += sizeof(struct udphdr);
        }
-       if (session->mtu != 0) {
-               dev->mtu = session->mtu;
-               dev->needed_headroom += session->hdr_len;
-               return;
-       }
+
        lock_sock(tunnel->sock);
        l3_overhead = kernel_sock_ip_overhead(tunnel->sock);
        release_sock(tunnel->sock);
+
        if (l3_overhead == 0) {
                /* L3 Overhead couldn't be identified, this could be
                 * because tunnel->sock was NULL or the socket's
@@ -255,12 +252,12 @@ static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tunnel,
         */
        overhead += session->hdr_len + ETH_HLEN + l3_overhead;
 
-       /* If PMTU discovery was enabled, use discovered MTU on L2TP device */
-       mtu = l2tp_tunnel_dst_mtu(tunnel);
-       if (mtu)
+       mtu = l2tp_tunnel_dst_mtu(tunnel) - overhead;
+       if (mtu < dev->min_mtu || mtu > dev->max_mtu)
+               dev->mtu = ETH_DATA_LEN - overhead;
+       else
                dev->mtu = mtu;
-       session->mtu = dev->mtu - overhead;
-       dev->mtu = session->mtu;
+
        dev->needed_headroom += session->hdr_len;
 }
 

diff --git a/net/l2tp/l2tp_netlink.c b/net/l2tp/l2tp_netlink.c
index a7c4092..2e1e926 100644 (file)
--- a/net/l2tp/l2tp_netlink.c
+++ b/net/l2tp/l2tp_netlink.c
@@ -608,9 +608,6 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
        if (info->attrs[L2TP_ATTR_RECV_TIMEOUT])
                cfg.reorder_timeout = nla_get_msecs(info->attrs[L2TP_ATTR_RECV_TIMEOUT]);
 
-       if (info->attrs[L2TP_ATTR_MTU])
-               cfg.mtu = nla_get_u16(info->attrs[L2TP_ATTR_MTU]);
-
 #ifdef CONFIG_MODULES
        if (l2tp_nl_cmd_ops[cfg.pw_type] == NULL) {
                genl_unlock();
@@ -698,9 +695,6 @@ static int l2tp_nl_cmd_session_modify(struct sk_buff *skb, struct genl_info *inf
        if (info->attrs[L2TP_ATTR_RECV_TIMEOUT])
                session->reorder_timeout = nla_get_msecs(info->attrs[L2TP_ATTR_RECV_TIMEOUT]);
 
-       if (info->attrs[L2TP_ATTR_MTU])
-               session->mtu = nla_get_u16(info->attrs[L2TP_ATTR_MTU]);
-
        ret = l2tp_session_notify(&l2tp_nl_family, info,
                                  session, L2TP_CMD_SESSION_MODIFY);
 
@@ -730,8 +724,7 @@ static int l2tp_nl_session_send(struct sk_buff *skb, u32 portid, u32 seq, int fl
            nla_put_u32(skb, L2TP_ATTR_PEER_SESSION_ID,
                        session->peer_session_id) ||
            nla_put_u32(skb, L2TP_ATTR_DEBUG, session->debug) ||
-           nla_put_u16(skb, L2TP_ATTR_PW_TYPE, session->pwtype) ||
-           nla_put_u16(skb, L2TP_ATTR_MTU, session->mtu))
+           nla_put_u16(skb, L2TP_ATTR_PW_TYPE, session->pwtype))
                goto nla_put_failure;
 
        if ((session->ifname[0] &&