net: gro: convert four dev_net() calls

tcp4_check_fraglist_gro(), tcp6_check_fraglist_gro(),
udp4_gro_lookup_skb() and udp6_gro_lookup_skb()
assume RCU is held so that the net structure does not disappear.

Use dev_net_rcu() instead of dev_net() to get LOCKDEP support.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250301201424.2046477-5-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/tcp_offload.c

@@ -425,7 +425,7 @@ static void tcp4_check_fraglist_gro(struct list_head *head, struct sk_buff *skb,
 
 	inet_get_iif_sdif(skb, &iif, &sdif);
 	iph = skb_gro_network_header(skb);
-	net = dev_net(skb->dev);
+	net = dev_net_rcu(skb->dev);
 	sk = __inet_lookup_established(net, net->ipv4.tcp_death_row.hashinfo,
 				       iph->saddr, th->source,
 				       iph->daddr, ntohs(th->dest),

net/ipv4/udp_offload.c

@@ -630,7 +630,7 @@ static struct sock *udp4_gro_lookup_skb(struct sk_buff *skb, __be16 sport,
 					__be16 dport)
 {
 	const struct iphdr *iph = skb_gro_network_header(skb);
-	struct net *net = dev_net(skb->dev);
+	struct net *net = dev_net_rcu(skb->dev);
 	int iif, sdif;
 
 	inet_get_iif_sdif(skb, &iif, &sdif);

net/ipv6/tcpv6_offload.c

@@ -35,7 +35,7 @@ static void tcp6_check_fraglist_gro(struct list_head *head, struct sk_buff *skb,
 
 	inet6_get_iif_sdif(skb, &iif, &sdif);
 	hdr = skb_gro_network_header(skb);
-	net = dev_net(skb->dev);
+	net = dev_net_rcu(skb->dev);
 	sk = __inet6_lookup_established(net, net->ipv4.tcp_death_row.hashinfo,
 					&hdr->saddr, th->source,
 					&hdr->daddr, ntohs(th->dest),

net/ipv6/udp_offload.c

@@ -117,7 +117,7 @@ static struct sock *udp6_gro_lookup_skb(struct sk_buff *skb, __be16 sport,
 					__be16 dport)
 {
 	const struct ipv6hdr *iph = skb_gro_network_header(skb);
-	struct net *net = dev_net(skb->dev);
+	struct net *net = dev_net_rcu(skb->dev);
 	int iif, sdif;
 
 	inet6_get_iif_sdif(skb, &iif, &sdif);