inet: preserve const qualifier in inet_sk()

We can change inet_sk() to propagate const qualifier of its argument.

This should avoid some potential errors caused by accidental
(const -> not_const) promotion.

Other helpers like tcp_sk(), udp_sk(), raw_sk() will be handled
in separate patch series.

v2: use container_of_const() as advised by Jakub and Linus
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/netdev/20230315142841.3a2ac99a@kernel.org/
Link: https://lore.kernel.org/netdev/CAHk-=wiOf12nrYEF2vJMcucKjWPN-Ns_SW9fA7LwST_2Dzp7rw@mail.gmail.com/Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet_sock.h

@@ -305,10 +305,7 @@ static inline struct sock *skb_to_full_sk(const struct sk_buff *skb)
 	return sk_to_full_sk(skb->sk);
 }
 
-static inline struct inet_sock *inet_sk(const struct sock *sk)
-{
-	return (struct inet_sock *)sk;
-}
+#define inet_sk(ptr) container_of_const(ptr, struct inet_sock, sk)
 
 static inline void __inet_sk_copy_descendant(struct sock *sk_to,
 					     const struct sock *sk_from,

include/trace/events/sock.h

@@ -158,7 +158,7 @@ TRACE_EVENT(inet_sock_set_state,
 	),
 
 	TP_fast_assign(
-		struct inet_sock *inet = inet_sk(sk);
+		const struct inet_sock *inet = inet_sk(sk);
 		struct in6_addr *pin6;
 		__be32 *p32;
 
@@ -222,7 +222,7 @@ TRACE_EVENT(inet_sk_error_report,
 	),
 
 	TP_fast_assign(
-		struct inet_sock *inet = inet_sk(sk);
+		const struct inet_sock *inet = inet_sk(sk);
 		struct in6_addr *pin6;
 		__be32 *p32;
 

include/trace/events/tcp.h

@@ -67,7 +67,7 @@ DECLARE_EVENT_CLASS(tcp_event_sk_skb,
 	),
 
 	TP_fast_assign(
-		struct inet_sock *inet = inet_sk(sk);
+		const struct inet_sock *inet = inet_sk(sk);
 		__be32 *p32;
 
 		__entry->skbaddr = skb;

net/ipv4/ip_output.c

@@ -129,7 +129,8 @@ int ip_local_out(struct net *net, struct sock *sk, struct sk_buff *skb)
 }
 EXPORT_SYMBOL_GPL(ip_local_out);
 
-static inline int ip_select_ttl(struct inet_sock *inet, struct dst_entry *dst)
+static inline int ip_select_ttl(const struct inet_sock *inet,
+				const struct dst_entry *dst)
 {
 	int ttl = inet->uc_ttl;
 
@@ -146,7 +147,7 @@ int ip_build_and_send_pkt(struct sk_buff *skb, const struct sock *sk,
 			  __be32 saddr, __be32 daddr, struct ip_options_rcu *opt,
 			  u8 tos)
 {
-	struct inet_sock *inet = inet_sk(sk);
+	const struct inet_sock *inet = inet_sk(sk);
 	struct rtable *rt = skb_rtable(skb);
 	struct net *net = sock_net(sk);
 	struct iphdr *iph;

net/ipv6/ping.c

@@ -237,7 +237,7 @@ static int ping_v6_seq_show(struct seq_file *seq, void *v)
 		seq_puts(seq, IPV6_SEQ_DGRAM_HEADER);
 	} else {
 		int bucket = ((struct ping_iter_state *) seq->private)->bucket;
-		struct inet_sock *inet = inet_sk(v);
+		struct inet_sock *inet = inet_sk((struct sock *)v);
 		__u16 srcp = ntohs(inet->inet_sport);
 		__u16 destp = ntohs(inet->inet_dport);
 		ip6_dgram_sock_seq_show(seq, v, srcp, destp, bucket);

net/ipv6/udp.c

@@ -1708,7 +1708,7 @@ int udp6_seq_show(struct seq_file *seq, void *v)
 		seq_puts(seq, IPV6_SEQ_DGRAM_HEADER);
 	} else {
 		int bucket = ((struct udp_iter_state *)seq->private)->bucket;
-		struct inet_sock *inet = inet_sk(v);
+		const struct inet_sock *inet = inet_sk((const struct sock *)v);
 		__u16 srcp = ntohs(inet->inet_sport);
 		__u16 destp = ntohs(inet->inet_dport);
 		__ip6_dgram_sock_seq_show(seq, v, srcp, destp,

net/mptcp/sockopt.c

@@ -1046,7 +1046,7 @@ static int mptcp_getsockopt_tcpinfo(struct mptcp_sock *msk, char __user *optval,
 
 static void mptcp_get_sub_addrs(const struct sock *sk, struct mptcp_subflow_addrs *a)
 {
-	struct inet_sock *inet = inet_sk(sk);
+	const struct inet_sock *inet = inet_sk(sk);
 
 	memset(a, 0, sizeof(*a));
 

security/lsm_audit.c

@@ -317,7 +317,7 @@ static void dump_common_audit_data(struct audit_buffer *ab,
 
 			switch (sk->sk_family) {
 			case AF_INET: {
-				struct inet_sock *inet = inet_sk(sk);
+				const struct inet_sock *inet = inet_sk(sk);
 
 				print_ipv4_addr(ab, inet->inet_rcv_saddr,
 						inet->inet_sport,
@@ -329,7 +329,7 @@ static void dump_common_audit_data(struct audit_buffer *ab,
 			}
 #if IS_ENABLED(CONFIG_IPV6)
 			case AF_INET6: {
-				struct inet_sock *inet = inet_sk(sk);
+				const struct inet_sock *inet = inet_sk(sk);
 
 				print_ipv6_addr(ab, &sk->sk_v6_rcv_saddr,
 						inet->inet_sport,