[PATCH 6.12.y 1/5] ipv6: start using dst_dev_rcu()

[Sasha Levin <sashal@kernel.org>]

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit b775ecf1655cedbc465fd6699ab18a2bc4e7a352 ]

Refactor icmpv6_xrlim_allow() and ip6_dst_hoplimit()
so that we acquire rcu_read_lock() a bit longer
to be able to use dst_dev_rcu() instead of dst_dev().

__ip6_rt_update_pmtu() and rt6_do_redirect can directly
use dst_dev_rcu() in sections already holding rcu_read_lock().

Small changes to use dst_dev_net_rcu() in
ip6_default_advmss(), ipv6_sock_ac_join(),
ip6_mc_find_dev() and ndisc_send_skb().

Fixes: 4a6ce2b6f2ec ("net: introduce a new function dst_dev_put()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20250828195823.3958522-3-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 2640e6419594 ("net: advertise TCP MSS from the configured MTU, not the learned PMTU")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/net/ip6_route.h | 3 +++
 net/ipv6/anycast.c      | 4 +++-
 net/ipv6/icmp.c         | 6 +++---
 net/ipv6/mcast.c        | 4 +++-
 net/ipv6/ndisc.c        | 2 +-
 net/ipv6/output_core.c  | 8 +++++---
 net/ipv6/route.c        | 9 ++++-----
 7 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index 59f48ca3abdf5..07c87c239511e 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -266,6 +266,9 @@ static inline bool ipv6_anycast_destination(const struct dst_entry *dst,
 int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 		 int (*output)(struct net *, struct sock *, struct sk_buff *));
 
+/* Compatibility form of the later IPv6-specific dst_mtu() wrapper. */
+#define dst6_mtu(dst) dst_mtu(dst)
+
 static inline unsigned int ip6_skb_dst_mtu(const struct sk_buff *skb)
 {
 	const struct ipv6_pinfo *np = skb->sk && !dev_recursion_level() ?
diff --git a/net/ipv6/anycast.c b/net/ipv6/anycast.c
index 0627c4c18d1a5..97c72dc541fd6 100644
--- a/net/ipv6/anycast.c
+++ b/net/ipv6/anycast.c
@@ -94,7 +94,9 @@ int ipv6_sock_ac_join(struct sock *sk, int ifindex, const struct in6_addr *addr)
 
 		rt = rt6_lookup(net, addr, NULL, 0, NULL, 0);
 		if (rt) {
-			dev = rt->dst.dev;
+			rcu_read_lock();
+			dev = dst_dev_rcu(&rt->dst);
+			rcu_read_unlock();
 			ip6_rt_put(rt);
 		} else if (ishost) {
 			err = -EADDRNOTAVAIL;
diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index 229ae205450d3..e4e40f0694238 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -209,7 +209,8 @@ static bool icmpv6_xrlim_allow(struct sock *sk, u8 type,
 	 * this lookup should be more aggressive (not longer than timeout).
 	 */
 	dst = ip6_route_output(net, sk, fl6);
-	dev = dst_dev(dst);
+	rcu_read_lock();
+	dev = dst_dev_rcu(dst);
 	if (dst->error) {
 		IP6_INC_STATS(net, ip6_dst_idev(dst),
 			      IPSTATS_MIB_OUTNOROUTES);
@@ -224,11 +225,10 @@ static bool icmpv6_xrlim_allow(struct sock *sk, u8 type,
 		if (rt->rt6i_dst.plen < 128)
 			tmo >>= ((128 - rt->rt6i_dst.plen)>>5);
 
-		rcu_read_lock();
 		peer = inet_getpeer_v6(net->ipv6.peers, &fl6->daddr);
 		res = inet_peer_xrlim_allow(peer, tmo);
-		rcu_read_unlock();
 	}
+	rcu_read_unlock();
 	if (!res)
 		__ICMP6_INC_STATS(net, ip6_dst_idev(dst),
 				  ICMP6_MIB_RATELIMITHOST);
diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 92f321635e4ec..335546d77f39c 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -201,7 +201,9 @@ static int __ipv6_sock_mc_join(struct sock *sk, int ifindex,
 		struct rt6_info *rt;
 		rt = rt6_lookup(net, addr, NULL, 0, NULL, 0);
 		if (rt) {
-			dev = rt->dst.dev;
+			rcu_read_lock();
+			dev = dst_dev_rcu(&rt->dst);
+			rcu_read_unlock();
 			ip6_rt_put(rt);
 		}
 	} else
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 87bed84a00532..26ad7cab0383f 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -508,7 +508,7 @@ void ndisc_send_skb(struct sk_buff *skb, const struct in6_addr *daddr,
 
 	ip6_nd_hdr(skb, saddr, daddr, READ_ONCE(inet6_sk(sk)->hop_limit), skb->len);
 
-	dev = dst_dev(dst);
+	dev = dst_dev_rcu(dst);
 	idev = __in6_dev_get(dev);
 	IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTREQUESTS);
 
diff --git a/net/ipv6/output_core.c b/net/ipv6/output_core.c
index 90a178dd24aae..5be101401a00e 100644
--- a/net/ipv6/output_core.c
+++ b/net/ipv6/output_core.c
@@ -104,18 +104,20 @@ EXPORT_SYMBOL(ip6_find_1stfragopt);
 int ip6_dst_hoplimit(struct dst_entry *dst)
 {
 	int hoplimit = dst_metric_raw(dst, RTAX_HOPLIMIT);
+
+	rcu_read_lock();
 	if (hoplimit == 0) {
-		struct net_device *dev = dst_dev(dst);
+		struct net_device *dev = dst_dev_rcu(dst);
 		struct inet6_dev *idev;
 
-		rcu_read_lock();
 		idev = __in6_dev_get(dev);
 		if (idev)
 			hoplimit = READ_ONCE(idev->cnf.hop_limit);
 		else
 			hoplimit = READ_ONCE(dev_net(dev)->ipv6.devconf_all->hop_limit);
-		rcu_read_unlock();
 	}
+	rcu_read_unlock();
+
 	return hoplimit;
 }
 EXPORT_SYMBOL(ip6_dst_hoplimit);
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index e602dd3e7ee39..eb2ba7c34f6f8 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2949,7 +2949,7 @@ static void __ip6_rt_update_pmtu(struct dst_entry *dst, const struct sock *sk,
 
 		if (res.f6i->nh) {
 			struct fib6_nh_match_arg arg = {
-				.dev = dst_dev(dst),
+				.dev = dst_dev_rcu(dst),
 				.gw = &rt6->rt6i_gateway,
 			};
 
@@ -3244,15 +3244,14 @@ EXPORT_SYMBOL_GPL(ip6_sk_redirect);
 
 static unsigned int ip6_default_advmss(const struct dst_entry *dst)
 {
-	struct net_device *dev = dst_dev(dst);
-	unsigned int mtu = dst_mtu(dst);
+	unsigned int mtu = dst6_mtu(dst);
 	struct net *net;
 
 	mtu -= sizeof(struct ipv6hdr) + sizeof(struct tcphdr);
 
 	rcu_read_lock();
 
-	net = dev_net_rcu(dev);
+	net = dst_dev_net_rcu(dst);
 	if (mtu < net->ipv6.sysctl.ip6_rt_min_advmss)
 		mtu = net->ipv6.sysctl.ip6_rt_min_advmss;
 
@@ -4266,7 +4265,7 @@ static void rt6_do_redirect(struct dst_entry *dst, struct sock *sk, struct sk_bu
 
 	if (res.f6i->nh) {
 		struct fib6_nh_match_arg arg = {
-			.dev = dst_dev(dst),
+			.dev = dst_dev_rcu(dst),
 			.gw = &rt->rt6i_gateway,
 		};
 
-- 
2.53.0