ipv4: add RCU protection to ip4_dst_hoplimit()

ip4_dst_hoplimit() must use RCU protection to make
sure the net structure it reads does not disappear.

Fixes: fa50d974d104 ("ipv4: Namespaceify ip_default_ttl sysctl knob")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250205155120.1676781-3-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/route.h b/include/net/route.h
index f86775be3e2934697533a61f566aca1ef196d74e..c605fd5ec0c08cc7658c3cf6aa6223790d463ede 100644 (file)
--- a/include/net/route.h
+++ b/include/net/route.h
@@ -382,10 +382,15 @@ static inline int inet_iif(const struct sk_buff *skb)
 static inline int ip4_dst_hoplimit(const struct dst_entry *dst)
 {
        int hoplimit = dst_metric_raw(dst, RTAX_HOPLIMIT);
-       struct net *net = dev_net(dst->dev);
 
-       if (hoplimit == 0)
+       if (hoplimit == 0) {
+               const struct net *net;
+
+               rcu_read_lock();
+               net = dev_net_rcu(dst->dev);
                hoplimit = READ_ONCE(net->ipv4.sysctl_ip_default_ttl);
+               rcu_read_unlock();
+       }
        return hoplimit;
 }