netdev - [PATCH net-next 8/8] ipv4: start using dst_dev

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Message-ID: <20250828195823.3958522-9-edumazet@google.com>
Date: Thu, 28 Aug 2025 19:58:23 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Neal Cardwell <ncardwell@...gle.com>
Cc: Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...gle.com>, 
	David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 8/8] ipv4: start using dst_dev_rcu()

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@...gle.com>
---
 net/ipv4/icmp.c        | 6 +++---
 net/ipv4/ip_fragment.c | 6 ++++--
 net/ipv4/ipmr.c        | 6 +++---
 net/ipv4/route.c       | 4 ++--
 4 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 7248c15cbd7592268dce883482727c994110dae8..823c70e34de835e78f58a7322e502324c795df86 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -319,17 +319,17 @@ 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 b2584cce90ae1c14550396de486131b700d4afd7..f7012479713ba68db7c1c3fcee07a86141de31d3 100644
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -476,14 +476,16 @@ 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 */
 	rcu_read_lock();
+	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, refs = 0;
diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 345e5faac63471249540fa77cb11fb2de50fd323..ca9eaee4c2ef5f5cdc03608291ad1a0dc187d657 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -1905,7 +1905,7 @@ static int ipmr_prepare_xmit(struct net *net, struct mr_table *mrt,
 		return -1;
 	}
 
-	encap += LL_RESERVED_SPACE(rt->dst.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);
@@ -1958,7 +1958,7 @@ static void ipmr_queue_fwd_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, rt->dst.dev,
+		net, NULL, skb, skb->dev, dst_dev_rcu(&rt->dst),
 		ipmr_forward_finish);
 	return;
 
@@ -2302,7 +2302,7 @@ int ip_mr_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 
 	guard(rcu)();
 
-	dev = rt->dst.dev;
+	dev = dst_dev_rcu(&rt->dst);
 
 	if (IPCB(skb)->flags & IPSKB_FORWARDED)
 		goto mc_output;
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index c63feef55d5193aadd11f9d5b45c8f5482e06be5..42f49187d3760330d0e0ca9e2c5fff778899f5fd 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -414,11 +414,11 @@ 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) {
-- 
2.51.0.318.gd7df087d1a-goog