netdev - [PATCH net 02/16] ipv4: add RCU protection to ip4_dst

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Message-ID: <20250131171334.1172661-3-edumazet@google.com>
Date: Fri, 31 Jan 2025 17:13:20 +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 net 02/16] 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@...gle.com>
---
 include/net/route.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/net/route.h b/include/net/route.h
index f86775be3e2934697533a61f566aca1ef196d74e..c605fd5ec0c08cc7658c3cf6aa6223790d463ede 100644
--- 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;
 }
 
-- 
2.48.1.362.g079036d154-goog