Patch "ipv4: use RCU protection in __ip_rt_update_pmtu()" has been added to the 6.13-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ipv4: use RCU protection in __ip_rt_update_pmtu()

to the 6.13-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ipv4-use-rcu-protection-in-__ip_rt_update_pmtu.patch
and it can be found in the queue-6.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 85003d41b2397dc27b26b76237142f39eaaede8c
Author: Eric Dumazet <edumazet@xxxxxxxxxx>
Date:   Wed Feb 5 15:51:15 2025 +0000

    ipv4: use RCU protection in __ip_rt_update_pmtu()
    
    [ Upstream commit 139512191bd06f1b496117c76372b2ce372c9a41 ]
    
    __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@xxxxxxxxxx>
    Link: https://patch.msgid.link/20250205155120.1676781-8-edumazet@xxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 152697459e918..cf84704af25c3 100644
--- 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();
 }