ipv4: Don't report stale pmtu values to userspace

We report cached pmtu values even if they are already expired.
Change this to not report these values after they are expired
and fix a race in the expire time calculation, as suggested by
Eric Dumazet.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 8 deletions

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 741df67a81ec..132e0dfee53a 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2187,8 +2187,18 @@ static int rt_fill_info(struct net *net,  __be32 dst, __be32 src,
             nla_put_be32(skb, RTA_GATEWAY, rt->rt_gateway))
                 goto nla_put_failure;
 
+        expires = rt->dst.expires;
+        if (expires) {
+                unsigned long now = jiffies;
+
+                if (time_before(now, expires))
+                        expires -= now;
+                else
+                        expires = 0;
+        }
+
         memcpy(metrics, dst_metrics_ptr(&rt->dst), sizeof(metrics));
-        if (rt->rt_pmtu)
+        if (rt->rt_pmtu && expires)
                 metrics[RTAX_MTU - 1] = rt->rt_pmtu;
         if (rtnetlink_put_metrics(skb, metrics) < 0)
                 goto nla_put_failure;
@@ -2198,13 +2208,6 @@ static int rt_fill_info(struct net *net,  __be32 dst, __be32 src,
                 goto nla_put_failure;
 
         error = rt->dst.error;
-        expires = rt->dst.expires;
-        if (expires) {
-                if (time_before(jiffies, expires))
-                        expires -= jiffies;
-                else
-                        expires = 0;
-        }
 
         if (rt_is_input_route(rt)) {
                 if (nla_put_u32(skb, RTA_IIF, rt->rt_iif))