[Openvpn-devel] [PATCH] Fix --mtu-disc option with IPv6 transport

[Julien Muchembled]

Socket configuration of MTU discovery was done unconditionally at IP level,
which has no effect for other protocols. This fixes the issue of OpenVPN
sending fragmented tcp6/udp6 packets even when 'mtu-disc yes' option is passed.

Signed-off-by: Julien Muchembled <j...@nexedi.com>
---
 src/openvpn/mtu.c    | 23 +++++++++++++++++------
 src/openvpn/mtu.h    |  2 +-
 src/openvpn/socket.c |  2 +-
 3 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/src/openvpn/mtu.c b/src/openvpn/mtu.c
index 13f3f6c..426c487 100644
--- a/src/openvpn/mtu.c
+++ b/src/openvpn/mtu.c
@@ -153,15 +153,26 @@ frame_print (const struct frame *frame,
 #define MTUDISC_NOT_SUPPORTED_MSG "--mtu-disc is not supported on this OS"

 void
-set_mtu_discover_type (int sd, int mtu_type)
+set_mtu_discover_type (int sd, int mtu_type, sa_family_t proto_af)
 {
   if (mtu_type >= 0)
     {
-#if defined(HAVE_SETSOCKOPT) && defined(SOL_IP) && defined(IP_MTU_DISCOVER)
-      if (setsockopt
-         (sd, SOL_IP, IP_MTU_DISCOVER, &mtu_type, sizeof (mtu_type)))
-       msg (M_ERR, "Error setting IP_MTU_DISCOVER type=%d on TCP/UDP socket",
-            mtu_type);
+#if defined(HAVE_SETSOCKOPT) && defined(IP_MTU_DISCOVER) && 
defined(IPV6_MTU_DISCOVER)
+      switch (proto_af)
+       {
+       case AF_INET:
+         if (setsockopt
+             (sd, IPPROTO_IP, IP_MTU_DISCOVER, &mtu_type, sizeof (mtu_type)))
+           msg (M_ERR, "Error setting IP_MTU_DISCOVER type=%d on TCP/UDP 
socket",
+                mtu_type);
+         break;
+       case AF_INET6:
+         if (setsockopt
+             (sd, IPPROTO_IPV6, IPV6_MTU_DISCOVER, &mtu_type, sizeof 
(mtu_type)))
+           msg (M_ERR, "Error setting IPV6_MTU_DISCOVER type=%d on TCP6/UDP6 
socket",
+                mtu_type);
+         break;
+       }
 #else
       msg (M_FATAL, MTUDISC_NOT_SUPPORTED_MSG);
 #endif
diff --git a/src/openvpn/mtu.h b/src/openvpn/mtu.h
index 29ec21f..cb41dc6 100644
--- a/src/openvpn/mtu.h
+++ b/src/openvpn/mtu.h
@@ -207,7 +207,7 @@ void frame_print (const struct frame *frame,
                  int level,
                  const char *prefix);

-void set_mtu_discover_type (int sd, int mtu_type);
+void set_mtu_discover_type (int sd, int mtu_type, sa_family_t proto_af);
 int translate_mtu_discover_type_name (const char *name);

 /*
diff --git a/src/openvpn/socket.c b/src/openvpn/socket.c
index 9e6bd10..344a9f7 100644
--- a/src/openvpn/socket.c
+++ b/src/openvpn/socket.c
@@ -1685,7 +1685,7 @@ phase2_set_socket_flags (struct link_socket* sock)
     set_cloexec (sock->ctrl_sd);

   /* set Path MTU discovery options on the socket */
-  set_mtu_discover_type (sock->sd, sock->mtu_discover_type);
+  set_mtu_discover_type (sock->sd, sock->mtu_discover_type, sock->info.af);

 #if EXTENDED_SOCKET_ERROR_CAPABILITY
   /* if the OS supports it, enable extended error passing on the socket */
-- 
1.8.5.2.988.g9b015e5.dirty