ipv4: icmp: convert to dev_net_rcu()

__icmp_send() must ensure rcu_read_lock() is held, as spotted
by Jakub.

Other ICMP uses of dev_net() seem safe, change them to dev_net_rcu()
to get LOCKDEP support.

Fixes: dde1bc0 ("[NETNS]: Add namespace for ICMP replying code.")
Closes: https://lore.kernel.org/netdev/[email protected]/
Reported-by: Jakub Kicinski <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: edumazet

net/ipv4/icmp.c

@@ -399,10 +399,10 @@ static void icmp_push_reply(struct sock *sk,
 
 static void icmp_reply(struct icmp_bxm *icmp_param, struct sk_buff *skb)
 {
-	struct ipcm_cookie ipc;
 	struct rtable *rt = skb_rtable(skb);
-	struct net *net = dev_net(rt->dst.dev);
+	struct net *net = dev_net_rcu(rt->dst.dev);
 	bool apply_ratelimit = false;
+	struct ipcm_cookie ipc;
 	struct flowi4 fl4;
 	struct sock *sk;
 	struct inet_sock *inet;
@@ -608,12 +608,14 @@ void __icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info,
 	struct sock *sk;
 
 	if (!rt)
-		goto out;
+		return;
+
+	rcu_read_lock();
 
 	if (rt->dst.dev)
-		net = dev_net(rt->dst.dev);
+		net = dev_net_rcu(rt->dst.dev);
 	else if (skb_in->dev)
-		net = dev_net(skb_in->dev);
+		net = dev_net_rcu(skb_in->dev);
 	else
 		goto out;
 
@@ -785,7 +787,8 @@ void __icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info,
 	icmp_xmit_unlock(sk);
 out_bh_enable:
 	local_bh_enable();
-out:;
+out:
+	rcu_read_unlock();
 }
 EXPORT_SYMBOL(__icmp_send);
 
@@ -834,7 +837,7 @@ static void icmp_socket_deliver(struct sk_buff *skb, u32 info)
 	 * avoid additional coding at protocol handlers.
 	 */
 	if (!pskb_may_pull(skb, iph->ihl * 4 + 8)) {
-		__ICMP_INC_STATS(dev_net(skb->dev), ICMP_MIB_INERRORS);
+		__ICMP_INC_STATS(dev_net_rcu(skb->dev), ICMP_MIB_INERRORS);
 		return;
 	}
 
@@ -868,7 +871,7 @@ static enum skb_drop_reason icmp_unreach(struct sk_buff *skb)
 	struct net *net;
 	u32 info = 0;
 
-	net = dev_net(skb_dst(skb)->dev);
+	net = dev_net_rcu(skb_dst(skb)->dev);
 
 	/*
 	 *	Incomplete header ?
@@ -979,7 +982,7 @@ static enum skb_drop_reason icmp_unreach(struct sk_buff *skb)
 static enum skb_drop_reason icmp_redirect(struct sk_buff *skb)
 {
 	if (skb->len < sizeof(struct iphdr)) {
-		__ICMP_INC_STATS(dev_net(skb->dev), ICMP_MIB_INERRORS);
+		__ICMP_INC_STATS(dev_net_rcu(skb->dev), ICMP_MIB_INERRORS);
 		return SKB_DROP_REASON_PKT_TOO_SMALL;
 	}
 
@@ -1011,7 +1014,7 @@ static enum skb_drop_reason icmp_echo(struct sk_buff *skb)
 	struct icmp_bxm icmp_param;
 	struct net *net;
 
-	net = dev_net(skb_dst(skb)->dev);
+	net = dev_net_rcu(skb_dst(skb)->dev);
 	/* should there be an ICMP stat for ignored echos? */
 	if (READ_ONCE(net->ipv4.sysctl_icmp_echo_ignore_all))
 		return SKB_NOT_DROPPED_YET;
@@ -1040,9 +1043,9 @@ static enum skb_drop_reason icmp_echo(struct sk_buff *skb)
 
 bool icmp_build_probe(struct sk_buff *skb, struct icmphdr *icmphdr)
 {
+	struct net *net = dev_net_rcu(skb->dev);
 	struct icmp_ext_hdr *ext_hdr, _ext_hdr;
 	struct icmp_ext_echo_iio *iio, _iio;
-	struct net *net = dev_net(skb->dev);
 	struct inet6_dev *in6_dev;
 	struct in_device *in_dev;
 	struct net_device *dev;
@@ -1181,7 +1184,7 @@ static enum skb_drop_reason icmp_timestamp(struct sk_buff *skb)
 	return SKB_NOT_DROPPED_YET;
 
 out_err:
-	__ICMP_INC_STATS(dev_net(skb_dst(skb)->dev), ICMP_MIB_INERRORS);
+	__ICMP_INC_STATS(dev_net_rcu(skb_dst(skb)->dev), ICMP_MIB_INERRORS);
 	return SKB_DROP_REASON_PKT_TOO_SMALL;
 }
 
@@ -1198,7 +1201,7 @@ int icmp_rcv(struct sk_buff *skb)
 {
 	enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
 	struct rtable *rt = skb_rtable(skb);
-	struct net *net = dev_net(rt->dst.dev);
+	struct net *net = dev_net_rcu(rt->dst.dev);
 	struct icmphdr *icmph;
 
 	if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb)) {
@@ -1371,9 +1374,9 @@ int icmp_err(struct sk_buff *skb, u32 info)
 	struct iphdr *iph = (struct iphdr *)skb->data;
 	int offset = iph->ihl<<2;
 	struct icmphdr *icmph = (struct icmphdr *)(skb->data + offset);
+	struct net *net = dev_net_rcu(skb->dev);
 	int type = icmp_hdr(skb)->type;
 	int code = icmp_hdr(skb)->code;
-	struct net *net = dev_net(skb->dev);
 
 	/*
 	 * Use ping_err to handle all icmp errors except those