[PATCH 6.12.y] ipv4: start using dst_dev_rcu()

[Miguel Gazquez]

From: Eric Dumazet <edumazet@xxxxxxxxxx>

[ Upstream commit 6ad8de3cefdb6ffa6708b21c567df0dbf82c43a8 ]

Change icmpv4_xrlim_allow(), ip_defrag() to prevent possible UAF.

Change ipmr_prepare_xmit(), ipmr_queue_fwd_xmit(), ip_mr_output(),
ipv4_neigh_lookup() to use lockdep enabled dst_dev_rcu().

Fixes: 4a6ce2b6f2ec ("net: introduce a new function dst_dev_put()")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reviewed-by: David Ahern <dsahern@xxxxxxxxxx>
Link: https://patch.msgid.link/20250828195823.3958522-9-edumazet@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
[ minor modifications to fix conflict ]
Signed-off-by: Miguel Gazquez <miguel.gazquez@xxxxxxxxxxx>
---
 net/ipv4/icmp.c        | 6 +++---
 net/ipv4/ip_fragment.c | 6 ++++--
 net/ipv4/ipmr.c        | 4 ++--
 net/ipv4/route.c       | 4 ++--
 4 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index c7af8b914e13..1fc967a60bb9 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -320,17 +320,17 @@ static bool icmpv4_xrlim_allow(struct net *net, struct rtable *rt,
 		return true;
 
 	/* No rate limit on loopback */
-	dev = dst_dev(dst);
+	rcu_read_lock();
+	dev = dst_dev_rcu(dst);
 	if (dev && (dev->flags & IFF_LOOPBACK))
 		goto out;
 
-	rcu_read_lock();
 	peer = inet_getpeer_v4(net->ipv4.peers, fl4->daddr,
 			       l3mdev_master_ifindex_rcu(dev));
 	rc = inet_peer_xrlim_allow(peer,
 				   READ_ONCE(net->ipv4.sysctl_icmp_ratelimit));
-	rcu_read_unlock();
 out:
+	rcu_read_unlock();
 	if (!rc)
 		__ICMP_INC_STATS(net, ICMP_MIB_RATELIMITHOST);
 	else
diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
index d3abc84a6c02..790df2c5f747 100644
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -483,13 +483,15 @@ static int ip_frag_reasm(struct ipq *qp, struct sk_buff *skb,
 /* Process an incoming IP datagram fragment. */
 int ip_defrag(struct net *net, struct sk_buff *skb, u32 user)
 {
-	struct net_device *dev = skb->dev ? : skb_dst_dev(skb);
-	int vif = l3mdev_master_ifindex_rcu(dev);
+	struct net_device *dev;
 	struct ipq *qp;
+	int vif;
 
 	__IP_INC_STATS(net, IPSTATS_MIB_REASMREQDS);
 
 	/* Lookup (or create) queue header */
+	dev = skb->dev ? : skb_dst_dev_rcu(skb);
+	vif = l3mdev_master_ifindex_rcu(dev);
 	qp = ip_find(net, ip_hdr(skb), user, vif);
 	if (qp) {
 		int ret;
diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index de0d9cc7806a..ad0b922ebc73 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -1906,7 +1906,7 @@ static void ipmr_queue_xmit(struct net *net, struct mr_table *mrt,
 		goto out_free;
 	}
 
-	encap += LL_RESERVED_SPACE(dev) + rt->dst.header_len;
+	encap += LL_RESERVED_SPACE(dst_dev_rcu(&rt->dst)) + rt->dst.header_len;
 
 	if (skb_cow(skb, encap)) {
 		ip_rt_put(rt);
@@ -1943,7 +1943,7 @@ static void ipmr_queue_xmit(struct net *net, struct mr_table *mrt,
 	 * result in receiving multiple packets.
 	 */
 	NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD,
-		net, NULL, skb, skb->dev, dev,
+		net, NULL, skb, skb->dev, dst_dev_rcu(&rt->dst),
 		ipmr_forward_finish);
 	return;
 
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 4dce0de6ab89..0f31ae4da3d9 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -413,11 +413,11 @@ static struct neighbour *ipv4_neigh_lookup(const struct dst_entry *dst,
 					   const void *daddr)
 {
 	const struct rtable *rt = container_of(dst, struct rtable, dst);
-	struct net_device *dev = dst_dev(dst);
+	struct net_device *dev;
 	struct neighbour *n;
 
 	rcu_read_lock();
-
+	dev = dst_dev_rcu(dst);
 	if (likely(rt->rt_gw_family == AF_INET)) {
 		n = ip_neigh_gw4(dev, rt->rt_gw4);
 	} else if (rt->rt_gw_family == AF_INET6) {

---
base-commit: 7155f3c7a69b8480e785f2a4252d31df95daa8d1
change-id: 20260820-cve-2025-40074-b2b8c05342a1

Best regards,
--  
Miguel Gazquez <miguel.gazquez@xxxxxxxxxxx>