Commit d52e5a7e authored by Sabrina Dubroca's avatar Sabrina Dubroca Committed by David S. Miller
Browse files

ipv4: lock mtu in fnhe when received PMTU < net.ipv4.route.min_pmtu 



Prior to the rework of PMTU information storage in commit
2c8cec5c ("ipv4: Cache learned PMTU information in inetpeer."),
when a PMTU event advertising a PMTU smaller than
net.ipv4.route.min_pmtu was received, we would disable setting the DF
flag on packets by locking the MTU metric, and set the PMTU to
net.ipv4.route.min_pmtu.

Since then, we don't disable DF, and set PMTU to
net.ipv4.route.min_pmtu, so the intermediate router that has this link
with a small MTU will have to drop the packets.

This patch reestablishes pre-2.6.39 behavior by splitting
rtable->rt_pmtu into a bitfield with rt_mtu_locked and rt_pmtu.
rt_mtu_locked indicates that we shouldn't set the DF bit on that path,
and is checked in ip_dont_fragment().

One possible workaround is to set net.ipv4.route.min_pmtu to a value low
enough to accommodate the lowest MTU encountered.

Fixes: 2c8cec5c ("ipv4: Cache learned PMTU information in inetpeer.")
Signed-off-by: default avatarSabrina Dubroca <sd@queasysnail.net>
Reviewed-by: default avatarStefano Brivio <sbrivio@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 16c2e4db

include/net/ip.h

+9 −2
Original line number Diff line number Diff line
@@ -328,6 +328,13 @@ int ip_decrease_ttl(struct iphdr *iph) 
	return --iph->ttl;

}



static inline int ip_mtu_locked(const struct dst_entry *dst)

{

	const struct rtable *rt = (const struct rtable *)dst;



	return rt->rt_mtu_locked || dst_metric_locked(dst, RTAX_MTU);

}



static inline

int ip_dont_fragment(const struct sock *sk, const struct dst_entry *dst)

{
@@ -335,7 +342,7 @@ int ip_dont_fragment(const struct sock *sk, const struct dst_entry *dst) 


	return  pmtudisc == IP_PMTUDISC_DO ||

		(pmtudisc == IP_PMTUDISC_WANT &&

		 !(dst_metric_locked(dst, RTAX_MTU)));

		 !ip_mtu_locked(dst));

}



static inline bool ip_sk_accept_pmtu(const struct sock *sk)
@@ -361,7 +368,7 @@ static inline unsigned int ip_dst_mtu_maybe_forward(const struct dst_entry *dst, 
	struct net *net = dev_net(dst->dev);



	if (net->ipv4.sysctl_ip_fwd_use_pmtu ||

	    dst_metric_locked(dst, RTAX_MTU) ||

	    ip_mtu_locked(dst) ||

	    !forwarding)

		return dst_mtu(dst);

include/net/ip_fib.h

+1 −0
Original line number Diff line number Diff line
@@ -59,6 +59,7 @@ struct fib_nh_exception { 
	int				fnhe_genid;

	__be32				fnhe_daddr;

	u32				fnhe_pmtu;

	bool				fnhe_mtu_locked;

	__be32				fnhe_gw;

	unsigned long			fnhe_expires;

	struct rtable __rcu		*fnhe_rth_input;

include/net/route.h

+2 −1
Original line number Diff line number Diff line
@@ -63,7 +63,8 @@ struct rtable { 
	__be32			rt_gateway;



	/* Miscellaneous cached information */

	u32			rt_pmtu;

	u32			rt_mtu_locked:1,

				rt_pmtu:31;



	u32			rt_table_id;

net/ipv4/route.c

+19 −7
Original line number Diff line number Diff line
@@ -634,6 +634,7 @@ static inline u32 fnhe_hashfun(__be32 daddr) 
static void fill_route_from_fnhe(struct rtable *rt, struct fib_nh_exception *fnhe)

{

	rt->rt_pmtu = fnhe->fnhe_pmtu;

	rt->rt_mtu_locked = fnhe->fnhe_mtu_locked;

	rt->dst.expires = fnhe->fnhe_expires;



	if (fnhe->fnhe_gw) {
@@ -644,7 +645,7 @@ static void fill_route_from_fnhe(struct rtable *rt, struct fib_nh_exception *fnh 
}



static void update_or_create_fnhe(struct fib_nh *nh, __be32 daddr, __be32 gw,

				  u32 pmtu, unsigned long expires)

				  u32 pmtu, bool lock, unsigned long expires)

{

	struct fnhe_hash_bucket *hash;

	struct fib_nh_exception *fnhe;
@@ -681,8 +682,10 @@ static void update_or_create_fnhe(struct fib_nh *nh, __be32 daddr, __be32 gw, 
			fnhe->fnhe_genid = genid;

		if (gw)

			fnhe->fnhe_gw = gw;

		if (pmtu)

		if (pmtu) {

			fnhe->fnhe_pmtu = pmtu;

			fnhe->fnhe_mtu_locked = lock;

		}

		fnhe->fnhe_expires = max(1UL, expires);

		/* Update all cached dsts too */

		rt = rcu_dereference(fnhe->fnhe_rth_input);
@@ -706,6 +709,7 @@ static void update_or_create_fnhe(struct fib_nh *nh, __be32 daddr, __be32 gw, 
		fnhe->fnhe_daddr = daddr;

		fnhe->fnhe_gw = gw;

		fnhe->fnhe_pmtu = pmtu;

		fnhe->fnhe_mtu_locked = lock;

		fnhe->fnhe_expires = expires;



		/* Exception created; mark the cached routes for the nexthop
@@ -787,7 +791,8 @@ static void __ip_do_redirect(struct rtable *rt, struct sk_buff *skb, struct flow 
				struct fib_nh *nh = &FIB_RES_NH(res);



				update_or_create_fnhe(nh, fl4->daddr, new_gw,

						0, jiffies + ip_rt_gc_timeout);

						0, false,

						jiffies + ip_rt_gc_timeout);

			}

			if (kill_route)

				rt->dst.obsolete = DST_OBSOLETE_KILL;
@@ -1009,15 +1014,18 @@ static void __ip_rt_update_pmtu(struct rtable *rt, struct flowi4 *fl4, u32 mtu) 
{

	struct dst_entry *dst = &rt->dst;

	struct fib_result res;

	bool lock = false;



	if (dst_metric_locked(dst, RTAX_MTU))

	if (ip_mtu_locked(dst))

		return;



	if (ipv4_mtu(dst) < mtu)

		return;



	if (mtu < ip_rt_min_pmtu)

	if (mtu < ip_rt_min_pmtu) {

		lock = true;

		mtu = ip_rt_min_pmtu;

	}



	if (rt->rt_pmtu == mtu &&

	    time_before(jiffies, dst->expires - ip_rt_mtu_expires / 2))
@@ -1027,7 +1035,7 @@ static void __ip_rt_update_pmtu(struct rtable *rt, struct flowi4 *fl4, u32 mtu) 
	if (fib_lookup(dev_net(dst->dev), fl4, &res, 0) == 0) {

		struct fib_nh *nh = &FIB_RES_NH(res);



		update_or_create_fnhe(nh, fl4->daddr, 0, mtu,

		update_or_create_fnhe(nh, fl4->daddr, 0, mtu, lock,

				      jiffies + ip_rt_mtu_expires);

	}

	rcu_read_unlock();
@@ -1280,7 +1288,7 @@ static unsigned int ipv4_mtu(const struct dst_entry *dst) 


	mtu = READ_ONCE(dst->dev->mtu);



	if (unlikely(dst_metric_locked(dst, RTAX_MTU))) {

	if (unlikely(ip_mtu_locked(dst))) {

		if (rt->rt_uses_gateway && mtu > 576)

			mtu = 576;

	}
@@ -1521,6 +1529,7 @@ struct rtable *rt_dst_alloc(struct net_device *dev, 
		rt->rt_is_input = 0;

		rt->rt_iif = 0;

		rt->rt_pmtu = 0;

		rt->rt_mtu_locked = 0;

		rt->rt_gateway = 0;

		rt->rt_uses_gateway = 0;

		rt->rt_table_id = 0;
@@ -2546,6 +2555,7 @@ struct dst_entry *ipv4_blackhole_route(struct net *net, struct dst_entry *dst_or 
		rt->rt_is_input = ort->rt_is_input;

		rt->rt_iif = ort->rt_iif;

		rt->rt_pmtu = ort->rt_pmtu;

		rt->rt_mtu_locked = ort->rt_mtu_locked;



		rt->rt_genid = rt_genid_ipv4(net);

		rt->rt_flags = ort->rt_flags;
@@ -2648,6 +2658,8 @@ static int rt_fill_info(struct net *net, __be32 dst, __be32 src, u32 table_id, 
	memcpy(metrics, dst_metrics_ptr(&rt->dst), sizeof(metrics));

	if (rt->rt_pmtu && expires)

		metrics[RTAX_MTU - 1] = rt->rt_pmtu;

	if (rt->rt_mtu_locked && expires)

		metrics[RTAX_LOCK - 1] |= BIT(RTAX_MTU);

	if (rtnetlink_put_metrics(skb, metrics) < 0)

		goto nla_put_failure;

net/ipv4/xfrm4_policy.c

+1 −0
Original line number Diff line number Diff line
@@ -100,6 +100,7 @@ static int xfrm4_fill_dst(struct xfrm_dst *xdst, struct net_device *dev, 
	xdst->u.rt.rt_gateway = rt->rt_gateway;

	xdst->u.rt.rt_uses_gateway = rt->rt_uses_gateway;

	xdst->u.rt.rt_pmtu = rt->rt_pmtu;

	xdst->u.rt.rt_mtu_locked = rt->rt_mtu_locked;

	xdst->u.rt.rt_table_id = rt->rt_table_id;

	INIT_LIST_HEAD(&xdst->u.rt.rt_uncached);

	rt_add_uncached_list(&xdst->u.rt);

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