From: Eric Dumazet <edumazet@google.com>
Date: Wed, 5 Feb 2025 15:51:18 +0000 (+0000)
Subject: ipv6: use RCU protection in ip6_default_advmss()
X-Git-Tag: v6.1.129~31
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=84212387caadb211cd9dadd6fd5563bd37dc1f5e;p=thirdparty%2Fkernel%2Fstable.git

ipv6: use RCU protection in ip6_default_advmss()

[ Upstream commit 3c8ffcd248da34fc41e52a46e51505900115fc2a ]

ip6_default_advmss() needs rcu protection to make
sure the net structure it reads does not disappear.

Fixes: 5578689a4e3c ("[NETNS][IPV6] route6 - make route6 per namespace")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250205155120.1676781-11-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index f3268bac9f198..17918f411386a 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -3190,13 +3190,18 @@ static unsigned int ip6_default_advmss(const struct dst_entry *dst)
 {
 	struct net_device *dev = dst->dev;
 	unsigned int mtu = dst_mtu(dst);
-	struct net *net = dev_net(dev);
+	struct net *net;
 
 	mtu -= sizeof(struct ipv6hdr) + sizeof(struct tcphdr);
 
+	rcu_read_lock();
+
+	net = dev_net_rcu(dev);
 	if (mtu < net->ipv6.sysctl.ip6_rt_min_advmss)
 		mtu = net->ipv6.sysctl.ip6_rt_min_advmss;
 
+	rcu_read_unlock();
+
 	/*
 	 * Maximal non-jumbo IPv6 payload is IPV6_MAXPLEN and
 	 * corresponding MSS is IPV6_MAXPLEN - tcp_header_size.