ipv4: use RCU protection in __ip_rt_update_pmtu()

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

Fixes: 2fbc6e89b2f1 ("ipv4: Update exception handling for multipath routes via same device")
Fixes: 1de6b15a434c ("Namespaceify min_pmtu sysctl")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250205155120.1676781-8-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index e959327c0ba8979ce5c7ca8c46ae41068824edc6..753704f75b2c65d79c9c4dc19a329de5cdbd8514 100644 (file)
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1008,9 +1008,9 @@ out:      kfree_skb_reason(skb, reason);
 static void __ip_rt_update_pmtu(struct rtable *rt, struct flowi4 *fl4, u32 mtu)
 {
        struct dst_entry *dst = &rt->dst;
-       struct net *net = dev_net(dst->dev);
        struct fib_result res;
        bool lock = false;
+       struct net *net;
        u32 old_mtu;
 
        if (ip_mtu_locked(dst))
@@ -1020,6 +1020,8 @@ static void __ip_rt_update_pmtu(struct rtable *rt, struct flowi4 *fl4, u32 mtu)
        if (old_mtu < mtu)
                return;
 
+       rcu_read_lock();
+       net = dev_net_rcu(dst->dev);
        if (mtu < net->ipv4.ip_rt_min_pmtu) {
                lock = true;
                mtu = min(old_mtu, net->ipv4.ip_rt_min_pmtu);
@@ -1027,9 +1029,8 @@ static void __ip_rt_update_pmtu(struct rtable *rt, struct flowi4 *fl4, u32 mtu)
 
        if (rt->rt_pmtu == mtu && !lock &&
            time_before(jiffies, dst->expires - net->ipv4.ip_rt_mtu_expires / 2))
-               return;
+               goto out;
 
-       rcu_read_lock();
        if (fib_lookup(net, fl4, &res, 0) == 0) {
                struct fib_nh_common *nhc;
 
@@ -1043,14 +1044,14 @@ static void __ip_rt_update_pmtu(struct rtable *rt, struct flowi4 *fl4, u32 mtu)
                                update_or_create_fnhe(nhc, fl4->daddr, 0, mtu, lock,
                                                      jiffies + net->ipv4.ip_rt_mtu_expires);
                        }
-                       rcu_read_unlock();
-                       return;
+                       goto out;
                }
 #endif /* CONFIG_IP_ROUTE_MULTIPATH */
                nhc = FIB_RES_NHC(res);
                update_or_create_fnhe(nhc, fl4->daddr, 0, mtu, lock,
                                      jiffies + net->ipv4.ip_rt_mtu_expires);
        }
+out:
        rcu_read_unlock();
 }