net: pmtu_expires fixes

commit 2c8cec5c10bc (ipv4: Cache learned PMTU information in inetpeer)
added some racy peer->pmtu_expires accesses.

As its value can be changed by another cpu/thread, we should be more
careful, reading its value once.

Add peer_pmtu_expired() and peer_pmtu_cleaned() helpers

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 44 insertions, 34 deletions

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 52b0b956508b..045f0ec6a4a0 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1316,6 +1316,23 @@ reject_redirect:
         ;
 }
 
+static bool peer_pmtu_expired(struct inet_peer *peer)
+{
+        unsigned long orig = ACCESS_ONCE(peer->pmtu_expires);
+
+        return orig &&
+               time_after_eq(jiffies, orig) &&
+               cmpxchg(&peer->pmtu_expires, orig, 0) == orig;
+}
+
+static bool peer_pmtu_cleaned(struct inet_peer *peer)
+{
+        unsigned long orig = ACCESS_ONCE(peer->pmtu_expires);
+
+        return orig &&
+               cmpxchg(&peer->pmtu_expires, orig, 0) == orig;
+}
+
 static struct dst_entry *ipv4_negative_advice(struct dst_entry *dst)
 {
         struct rtable *rt = (struct rtable *)dst;
@@ -1331,14 +1348,8 @@ static struct dst_entry *ipv4_negative_advice(struct dst_entry *dst)
                                                 rt_genid(dev_net(dst->dev)));
                         rt_del(hash, rt);
                         ret = NULL;
-                } else if (rt->peer &&
-                           rt->peer->pmtu_expires &&
-                           time_after_eq(jiffies, rt->peer->pmtu_expires)) {
-                        unsigned long orig = rt->peer->pmtu_expires;
-
-                        if (cmpxchg(&rt->peer->pmtu_expires, orig, 0) == orig)
-                                dst_metric_set(dst, RTAX_MTU,
-                                               rt->peer->pmtu_orig);
+                } else if (rt->peer && peer_pmtu_expired(rt->peer)) {
+                        dst_metric_set(dst, RTAX_MTU, rt->peer->pmtu_orig);
                 }
         }
         return ret;
@@ -1531,8 +1542,10 @@ unsigned short ip_rt_frag_needed(struct net *net, const struct iphdr *iph,
 
 static void check_peer_pmtu(struct dst_entry *dst, struct inet_peer *peer)
 {
-        unsigned long expires = peer->pmtu_expires;
+        unsigned long expires = ACCESS_ONCE(peer->pmtu_expires);
 
+        if (!expires)
+                return;
         if (time_before(jiffies, expires)) {
                 u32 orig_dst_mtu = dst_mtu(dst);
                 if (peer->pmtu_learned < orig_dst_mtu) {
@@ -1555,10 +1568,11 @@ static void ip_rt_update_pmtu(struct dst_entry *dst, u32 mtu)
                 rt_bind_peer(rt, rt->rt_dst, 1);
         peer = rt->peer;
         if (peer) {
+                unsigned long pmtu_expires = ACCESS_ONCE(peer->pmtu_expires);
+
                 if (mtu < ip_rt_min_pmtu)
                         mtu = ip_rt_min_pmtu;
-                if (!peer->pmtu_expires || mtu < peer->pmtu_learned) {
-                        unsigned long pmtu_expires;
+                if (!pmtu_expires || mtu < peer->pmtu_learned) {
 
                         pmtu_expires = jiffies + ip_rt_mtu_expires;
                         if (!pmtu_expires)
@@ -1612,13 +1626,14 @@ static struct dst_entry *ipv4_dst_check(struct dst_entry *dst, u32 cookie)
                         rt_bind_peer(rt, rt->rt_dst, 0);
 
                 peer = rt->peer;
-                if (peer && peer->pmtu_expires)
+                if (peer) {
                         check_peer_pmtu(dst, peer);
 
-                if (peer && peer->redirect_learned.a4 &&
-                    peer->redirect_learned.a4 != rt->rt_gateway) {
-                        if (check_peer_redir(dst, peer))
-                                return NULL;
+                        if (peer->redirect_learned.a4 &&
+                            peer->redirect_learned.a4 != rt->rt_gateway) {
+                                if (check_peer_redir(dst, peer))
+                                        return NULL;
+                        }
                 }
 
                 rt->rt_peer_genid = rt_peer_genid();
@@ -1649,14 +1664,8 @@ static void ipv4_link_failure(struct sk_buff *skb)
         icmp_send(skb, ICMP_DEST_UNREACH, ICMP_HOST_UNREACH, 0);
 
         rt = skb_rtable(skb);
-        if (rt &&
-            rt->peer &&
-            rt->peer->pmtu_expires) {
-                unsigned long orig = rt->peer->pmtu_expires;
-
-                if (cmpxchg(&rt->peer->pmtu_expires, orig, 0) == orig)
-                        dst_metric_set(&rt->dst, RTAX_MTU, rt->peer->pmtu_orig);
-        }
+        if (rt && rt->peer && peer_pmtu_cleaned(rt->peer))
+                dst_metric_set(&rt->dst, RTAX_MTU, rt->peer->pmtu_orig);
 }
 
 static int ip_rt_bug(struct sk_buff *skb)
@@ -1770,8 +1779,7 @@ static void rt_init_metrics(struct rtable *rt, const struct flowi4 *fl4,
                                sizeof(u32) * RTAX_MAX);
                 dst_init_metrics(&rt->dst, peer->metrics, false);
 
-                if (peer->pmtu_expires)
-                        check_peer_pmtu(&rt->dst, peer);
+                check_peer_pmtu(&rt->dst, peer);
                 if (peer->redirect_learned.a4 &&
                     peer->redirect_learned.a4 != rt->rt_gateway) {
                         rt->rt_gateway = peer->redirect_learned.a4;
@@ -2775,7 +2783,8 @@ static int rt_fill_info(struct net *net,
         struct rtable *rt = skb_rtable(skb);
         struct rtmsg *r;
         struct nlmsghdr *nlh;
-        long expires;
+        long expires = 0;
+        const struct inet_peer *peer = rt->peer;
         u32 id = 0, ts = 0, tsage = 0, error;
 
         nlh = nlmsg_put(skb, pid, seq, event, sizeof(*r), flags);
@@ -2823,15 +2832,16 @@ static int rt_fill_info(struct net *net,
                 NLA_PUT_BE32(skb, RTA_MARK, rt->rt_mark);
 
         error = rt->dst.error;
-        expires = (rt->peer && rt->peer->pmtu_expires) ?
-                rt->peer->pmtu_expires - jiffies : 0;
-        if (rt->peer) {
+        if (peer) {
                 inet_peer_refcheck(rt->peer);
-                id = atomic_read(&rt->peer->ip_id_count) & 0xffff;
-                if (rt->peer->tcp_ts_stamp) {
-                        ts = rt->peer->tcp_ts;
-                        tsage = get_seconds() - rt->peer->tcp_ts_stamp;
+                id = atomic_read(&peer->ip_id_count) & 0xffff;
+                if (peer->tcp_ts_stamp) {
+                        ts = peer->tcp_ts;
+                        tsage = get_seconds() - peer->tcp_ts_stamp;
                 }
+                expires = ACCESS_ONCE(peer->pmtu_expires);
+                if (expires)
+                        expires -= jiffies;
         }
 
         if (rt_is_input_route(rt)) {