netdev - [PATCH v4 net 07/12] ipv4: use RCU protection in __ip_rt_update

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Message-ID: <20250205155120.1676781-8-edumazet@google.com>
Date: Wed,  5 Feb 2025 15:51:15 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, Kuniyuki Iwashima <kuniyu@...zon.com>, 
	Simon Horman <horms@...nel.org>, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH v4 net 07/12] 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@...gle.com>
---
 net/ipv4/route.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index e959327c0ba8979ce5c7ca8c46ae41068824edc6..753704f75b2c65d79c9c4dc19a329de5cdbd8514 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();
 }
 
-- 
2.48.1.362.g079036d154-goog