From 113c3075931a334f899008f6c753abe70a3a9323 Mon Sep 17 00:00:00 2001
From: "R. Parameswaran" <parameswaran.r7@gmail.com>
Date: Wed, 5 Apr 2017 16:50:35 -0700
Subject: [PATCH 1/2] New kernel function to get IP overhead on a socket.
A new function, kernel_sock_ip_overhead(), is provided
to calculate the cumulative overhead imposed by the IP
Header and IP options, if any, on a socket's payload.
The new function returns an overhead of zero for sockets
that do not belong to the IPv4 or IPv6 address families.
This is used in the L2TP code path to compute the
total outer IP overhead on the L2TP tunnel socket when
calculating the default MTU for Ethernet pseudowires.
Signed-off-by: R. Parameswaran <rparames@brocade.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
include/linux/net.h | 3 +++
net/socket.c | 46 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 49 insertions(+)
diff --git a/include/linux/net.h b/include/linux/net.h
index 0620f5e18c96b..a42fab24c8af6 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -298,6 +298,9 @@ int kernel_sendpage(struct socket *sock, struct page *page, int offset,
int kernel_sock_ioctl(struct socket *sock, int cmd, unsigned long arg);
int kernel_sock_shutdown(struct socket *sock, enum sock_shutdown_cmd how);
+/* Following routine returns the IP overhead imposed by a socket. */
+u32 kernel_sock_ip_overhead(struct sock *sk);
+
#define MODULE_ALIAS_NETPROTO(proto) \
MODULE_ALIAS("net-pf-" __stringify(proto))
diff --git a/net/socket.c b/net/socket.c
index 985ef06792d6e..eea997036ada5 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -3356,3 +3356,49 @@ int kernel_sock_shutdown(struct socket *sock, enum sock_shutdown_cmd how)
return sock->ops->shutdown(sock, how);
}
EXPORT_SYMBOL(kernel_sock_shutdown);
+
+/* This routine returns the IP overhead imposed by a socket i.e.
+ * the length of the underlying IP header, depending on whether
+ * this is an IPv4 or IPv6 socket and the length from IP options turned
+ * on at the socket.
+ */
+u32 kernel_sock_ip_overhead(struct sock *sk)
+{
+ struct inet_sock *inet;
+ struct ip_options_rcu *opt;
+ u32 overhead = 0;
+ bool owned_by_user;
+#if IS_ENABLED(CONFIG_IPV6)
+ struct ipv6_pinfo *np;
+ struct ipv6_txoptions *optv6 = NULL;
+#endif /* IS_ENABLED(CONFIG_IPV6) */
+
+ if (!sk)
+ return overhead;
+
+ owned_by_user = sock_owned_by_user(sk);
+ switch (sk->sk_family) {
+ case AF_INET:
+ inet = inet_sk(sk);
+ overhead += sizeof(struct iphdr);
+ opt = rcu_dereference_protected(inet->inet_opt,
+ owned_by_user);
+ if (opt)
+ overhead += opt->opt.optlen;
+ return overhead;
+#if IS_ENABLED(CONFIG_IPV6)
+ case AF_INET6:
+ np = inet6_sk(sk);
+ overhead += sizeof(struct ipv6hdr);
+ if (np)
+ optv6 = rcu_dereference_protected(np->opt,
+ owned_by_user);
+ if (optv6)
+ overhead += (optv6->opt_flen + optv6->opt_nflen);
+ return overhead;
+#endif /* IS_ENABLED(CONFIG_IPV6) */
+ default: /* Returns 0 overhead if the socket is not ipv4 or ipv6 */
+ return overhead;
+ }
+}
+EXPORT_SYMBOL(kernel_sock_ip_overhead);
From b784e7ebfce8cfb16c6f95e14e8532d0768ab7ff Mon Sep 17 00:00:00 2001
From: "R. Parameswaran" <parameswaran.r7@gmail.com>
Date: Wed, 5 Apr 2017 17:00:07 -0700
Subject: [PATCH 2/2] L2TP:Adjust intf MTU, add underlay L3, L2 hdrs.
Existing L2TP kernel code does not derive the optimal MTU for Ethernet
pseudowires and instead leaves this to a userspace L2TP daemon or
operator. If an MTU is not specified, the existing kernel code chooses
an MTU that does not take account of all tunnel header overheads, which
can lead to unwanted IP fragmentation. When L2TP is used without a
control plane (userspace daemon), we would prefer that the kernel does a
better job of choosing a default pseudowire MTU, taking account of all
tunnel header overheads, including IP header options, if any. This patch
addresses this.
Change-set here uses the new kernel function, kernel_sock_ip_overhead(),
to factor the outer IP overhead on the L2TP tunnel socket (including
IP Options, if any) when calculating the default MTU for an Ethernet
pseudowire, along with consideration of the inner Ethernet header.
Signed-off-by: R. Parameswaran <rparames@brocade.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
net/l2tp/l2tp_eth.c | 55 +++++++++++++++++++++++++++++++++++++++++----
1 file changed, 51 insertions(+), 4 deletions(-)
diff --git a/net/l2tp/l2tp_eth.c b/net/l2tp/l2tp_eth.c
index 6fd41d7afe1ef..138566a631234 100644
--- a/net/l2tp/l2tp_eth.c
+++ b/net/l2tp/l2tp_eth.c
@@ -30,6 +30,9 @@
#include <net/xfrm.h>
#include <net/net_namespace.h>
#include <net/netns/generic.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include <linux/udp.h>
#include "l2tp_core.h"
@@ -204,6 +207,53 @@ static void l2tp_eth_show(struct seq_file *m, void *arg)
}
#endif
+static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tunnel,
+ struct l2tp_session *session,
+ struct net_device *dev)
+{
+ unsigned int overhead = 0;
+ struct dst_entry *dst;
+ u32 l3_overhead = 0;
+
+ /* if the encap is UDP, account for UDP header size */
+ if (tunnel->encap == L2TP_ENCAPTYPE_UDP) {
+ 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;
+ }
+ l3_overhead = kernel_sock_ip_overhead(tunnel->sock);
+ if (l3_overhead == 0) {
+ /* L3 Overhead couldn't be identified, this could be
+ * because tunnel->sock was NULL or the socket's
+ * address family was not IPv4 or IPv6,
+ * dev mtu stays at 1500.
+ */
+ return;
+ }
+ /* Adjust MTU, factor overhead - underlay L3, overlay L2 hdr
+ * UDP overhead, if any, was already factored in above.
+ */
+ overhead += session->hdr_len + ETH_HLEN + l3_overhead;
+
+ /* If PMTU discovery was enabled, use discovered MTU on L2TP device */
+ dst = sk_dst_get(tunnel->sock);
+ if (dst) {
+ /* dst_mtu will use PMTU if found, else fallback to intf MTU */
+ u32 pmtu = dst_mtu(dst);
+
+ if (pmtu != 0)
+ dev->mtu = pmtu;
+ dst_release(dst);
+ }
+ session->mtu = dev->mtu - overhead;
+ dev->mtu = session->mtu;
+ dev->needed_headroom += session->hdr_len;
+}
+
static int l2tp_eth_create(struct net *net, u32 tunnel_id, u32 session_id, u32 peer_session_id, struct l2tp_session_cfg *cfg)
{
struct net_device *dev;
@@ -247,12 +297,9 @@ static int l2tp_eth_create(struct net *net, u32 tunnel_id, u32 session_id, u32 p
}
dev_net_set(dev, net);
- if (session->mtu == 0)
- session->mtu = dev->mtu - session->hdr_len;
- dev->mtu = session->mtu;
- dev->needed_headroom += session->hdr_len;
dev->min_mtu = 0;
dev->max_mtu = ETH_MAX_MTU;
+ l2tp_eth_adjust_mtu(tunnel, session, dev);
priv = netdev_priv(dev);
priv->dev = dev;