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

Prior to the rework of PMTU information storage in commit
2c8cec5c10 ("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: 2c8cec5c10 ("ipv4: Cache learned PMTU information in inetpeer.")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Sabrina Dubroca 2018-03-14 10:21:14 +01:00 committed by David S. Miller
parent 16c2e4db83
commit d52e5a7e7c
5 changed files with 32 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
include/net/ip.h
View File

@ -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);

1
include/net/ip_fib.h
View File

@ -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;

3
include/net/route.h
View File

@ -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;

26
net/ipv4/route.c
View File

@ -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;

1
net/ipv4/xfrm4_policy.c
View File

@ -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);