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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>
This commit is contained in:
Guillaume Nault 2018-08-03 12:38:39 +02:00 committed by David S. Miller
parent 789141b215
commit e9697e2eff
6 changed files with 10 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/uapi/linux/l2tp.h
View File

@ -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 */

1
net/l2tp/l2tp_core.c
View File

@ -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;

2
net/l2tp/l2tp_core.h
View File

@ -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 */

3
net/l2tp/l2tp_debugfs.c
View File

@ -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",

17
net/l2tp/l2tp_eth.c
View File

@ -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;
}

9
net/l2tp/l2tp_netlink.c
View File

@ -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] &&