Commit e9697e2e authored by Guillaume Nault's avatar Guillaume Nault Committed by David S. Miller
Browse files

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: default avatarGuillaume Nault <g.nault@alphalink.fr>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 789141b2

include/uapi/linux/l2tp.h

+1 −1
Original line number Diff line number Diff line
@@ -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 */

net/l2tp/l2tp_core.c

+0 −1
Original line number Diff line number Diff line
@@ -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;

net/l2tp/l2tp_core.h

+0 −2
Original line number Diff line number Diff line
@@ -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 */

net/l2tp/l2tp_debugfs.c

+1 −2
Original line number Diff line number Diff line
@@ -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",

net/l2tp/l2tp_eth.c

+7 −10
Original line number Diff line number Diff line
@@ -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;

}

CRA Git | Maintained and supported by SUSTech CRA and CCSE