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>

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 52b0b95..045f0ec 100644 (file)
--- 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)) {