[net-2.6.13 3/3] [IPSEC] Add XFRM_STATE_NOPMTUDISC flag

[net-2.6.13 3/3] [IPSEC] Add XFRM_STATE_NOPMTUDISC flag

[Herbert Xu]

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Hi:

This patch adds the flag XFRM_STATE_NOPMTUDISC for xfrm states.  It is
similar to the nopmtudisc on IPIP/GRE tunnels.  It only has an effect
on IPv4 tunnel mode states.  For these states, it will ensure that the
DF flag is always cleared.

This is primarily useful to work around ICMP blackholes.

In future this flag could also allow a larger MTU to be set within the
tunnel just like IPIP/GRE tunnels.  This could be useful for short haul
tunnels where temporary fragmentation outside the tunnel is desired over
smaller fragments inside the tunnel.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

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diff --git a/include/linux/pfkeyv2.h b/include/linux/pfkeyv2.h
--- a/include/linux/pfkeyv2.h
+++ b/include/linux/pfkeyv2.h
@@ -245,6 +245,7 @@ struct sadb_x_nat_t_port {
 
 /* Security Association flags */
 #define SADB_SAFLAGS_PFS	1
+#define SADB_SAFLAGS_NOPMTUDISC	0x20000000
 #define SADB_SAFLAGS_DECAP_DSCP	0x40000000
 #define SADB_SAFLAGS_NOECN	0x80000000
 
diff --git a/include/linux/xfrm.h b/include/linux/xfrm.h
--- a/include/linux/xfrm.h
+++ b/include/linux/xfrm.h
@@ -196,6 +196,7 @@ struct xfrm_usersa_info {
 	__u8				flags;
 #define XFRM_STATE_NOECN	1
 #define XFRM_STATE_DECAP_DSCP	2
+#define XFRM_STATE_NOPMTUDISC	4
 };
 
 struct xfrm_usersa_id {
diff --git a/net/ipv4/xfrm4_output.c b/net/ipv4/xfrm4_output.c
--- a/net/ipv4/xfrm4_output.c
+++ b/net/ipv4/xfrm4_output.c
@@ -33,6 +33,7 @@ static void xfrm4_encap(struct sk_buff *
 	struct dst_entry *dst = skb->dst;
 	struct xfrm_state *x = dst->xfrm;
 	struct iphdr *iph, *top_iph;
+	int flags;
 
 	iph = skb->nh.iph;
 	skb->h.ipiph = iph;
@@ -51,10 +52,13 @@ static void xfrm4_encap(struct sk_buff *
 
 	/* DS disclosed */
 	top_iph->tos = INET_ECN_encapsulate(iph->tos, iph->tos);
-	if (x->props.flags & XFRM_STATE_NOECN)
+
+	flags = x->props.flags;
+	if (flags & XFRM_STATE_NOECN)
 		IP_ECN_clear(top_iph);
 
-	top_iph->frag_off = iph->frag_off & htons(IP_DF);
+	top_iph->frag_off = (flags & XFRM_STATE_NOPMTUDISC) ?
+		0 : (iph->frag_off & htons(IP_DF));
 	if (!top_iph->frag_off)
 		__ip_select_ident(top_iph, dst, 0);
 
diff --git a/net/ipv4/xfrm4_state.c b/net/ipv4/xfrm4_state.c
--- a/net/ipv4/xfrm4_state.c
+++ b/net/ipv4/xfrm4_state.c
@@ -7,12 +7,20 @@
  *
  */
 
+#include <net/ip.h>
 #include <net/xfrm.h>
 #include <linux/pfkeyv2.h>
 #include <linux/ipsec.h>
 
 static struct xfrm_state_afinfo xfrm4_state_afinfo;
 
+static int xfrm4_init_flags(struct xfrm_state *x)
+{
+	if (ipv4_config.no_pmtu_disc)
+		x->props.flags |= XFRM_STATE_NOPMTUDISC;
+	return 0;
+}
+
 static void
 __xfrm4_init_tempsel(struct xfrm_state *x, struct flowi *fl,
 		     struct xfrm_tmpl *tmpl,
@@ -109,6 +117,7 @@ __xfrm4_find_acq(u8 mode, u32 reqid, u8 
 static struct xfrm_state_afinfo xfrm4_state_afinfo = {
 	.family			= AF_INET,
 	.lock			= RW_LOCK_UNLOCKED,
+	.init_flags		= xfrm4_init_flags,
 	.init_tempsel		= __xfrm4_init_tempsel,
 	.state_lookup		= __xfrm4_state_lookup,
 	.find_acq		= __xfrm4_find_acq,
diff --git a/net/key/af_key.c b/net/key/af_key.c
--- a/net/key/af_key.c
+++ b/net/key/af_key.c
@@ -690,6 +690,8 @@ static struct sk_buff * pfkey_xfrm_state
 		sa->sadb_sa_flags |= SADB_SAFLAGS_NOECN;
 	if (x->props.flags & XFRM_STATE_DECAP_DSCP)
 		sa->sadb_sa_flags |= SADB_SAFLAGS_DECAP_DSCP;
+	if (x->props.flags & XFRM_STATE_NOPMTUDISC)
+		sa->sadb_sa_flags |= SADB_SAFLAGS_NOPMTUDISC;
 
 	/* hard time */
 	if (hsc & 2) {
@@ -974,6 +976,8 @@ static struct xfrm_state * pfkey_msg2xfr
 		x->props.flags |= XFRM_STATE_NOECN;
 	if (sa->sadb_sa_flags & SADB_SAFLAGS_DECAP_DSCP)
 		x->props.flags |= XFRM_STATE_DECAP_DSCP;
+	if (sa->sadb_sa_flags & SADB_SAFLAGS_NOPMTUDISC)
+		x->props.flags |= XFRM_STATE_NOPMTUDISC;
 
 	lifetime = (struct sadb_lifetime*) ext_hdrs[SADB_EXT_LIFETIME_HARD-1];
 	if (lifetime != NULL) {

Re: [net-2.6.13 0/3] [IPSEC] Allow PMTU discovery to be turned off

[David S. Miller]

From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Mon, 13 Jun 2005 17:33:53 +1000

> One of the problems that's been plaguing our IPsec stack is ICMP
> blackholes.  ICMP blackholes are particularly bad for tunnels because
> the most common remediy -- MSS clamping has no effect when applied
> outside the tunnel.  It is often impractical to apply it inside
> the tunnel since the point where the clamping is applied may be some
> way away from either IPsec endpoint.
> 
> The best solution so far has been to disable PMTU discovery when a
> blackhole is detected.  We already support that for IPIP/GRE tunnels.
> The following patchset adds support for a similar strategy to IPsec
> tunnels.
> 
> It is by no means ideal but it's something that you need to survive
> on today's Internet.

All 3 patches applied, thanks Herbert.

One thing needs clarification in your description.  When I first
read "blackhole is detected" I was under the wrong impression as
to _who_ does the detection.  Your patches allow the administrator
to do this, whereas I thought you were going to add some code which
dynamically figured out the presence of ICMP black holes and would
thus set the bit.