tcp/udp: Call inet6_destroy_sock() in IPv6 sk->sk_destruct().

Originally, inet6_sk(sk)->XXX were changed under lock_sock(), so we were
able to clean them up by calling inet6_destroy_sock() during the IPv6 ->
IPv4 conversion by IPV6_ADDRFORM. However, commit 03485f2adcde ("udpv6:
Add lockless sendmsg() support") added a lockless memory allocation path,
which could cause a memory leak:

setsockopt(IPV6_ADDRFORM) sendmsg()
+-----------------------+ +-------+
- do_ipv6_setsockopt(sk, ...) - udpv6_sendmsg(sk, ...)
- sockopt_lock_sock(sk) ^._ called via udpv6_prot
- lock_sock(sk) before WRITE_ONCE()
- WRITE_ONCE(sk->sk_prot, &tcp_prot)
- inet6_destroy_sock() - if (!corkreq)
- sockopt_release_sock(sk) - ip6_make_skb(sk, ...)
- release_sock(sk) ^._ lockless fast path for
the non-corking case

- __ip6_append_data(sk, ...)
- ipv6_local_rxpmtu(sk, ...)
- xchg(&np->rxpmtu, skb)
^._ rxpmtu is never freed.

- goto out_no_dst;

- lock_sock(sk)

For now, rxpmtu is only the case, but not to miss the future change
and a similar bug fixed in commit e27326009a3d ("net: ping6: Fix
memleak in ipv6_renew_options()."), let's set a new function to IPv6
sk->sk_destruct() and call inet6_cleanup_sock() there. Since the
conversion does not change sk->sk_destruct(), we can guarantee that
we can clean up IPv6 resources finally.

We can now remove all inet6_destroy_sock() calls from IPv6 protocol
specific ->destroy() functions, but such changes are invasive to
backport. So they can be posted as a follow-up later for net-next.

Fixes: 03485f2adcde ("udpv6: Add lockless sendmsg() support")
Signed-off-by: Kuniyuki Iwashima <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>

include/net/ipv6.h

···
 void ipv6_local_rxpmtu(struct sock *sk, struct flowi6 *fl6, u32 mtu);
 
 void inet6_cleanup_sock(struct sock *sk);
+void inet6_sock_destruct(struct sock *sk);
 int inet6_release(struct socket *sock);
 int inet6_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len);
 int inet6_getname(struct socket *sock, struct sockaddr *uaddr,

include/net/udp.h

···
 }
 
 /* net/ipv4/udp.c */
-void udp_destruct_sock(struct sock *sk);
+void udp_destruct_common(struct sock *sk);
 void skb_consume_udp(struct sock *sk, struct sk_buff *skb, int len);
 int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb);
 void udp_skb_destructor(struct sock *sk, struct sk_buff *skb);

include/net/udplite.h

···
 	return copy_from_iter_full(to, len, &msg->msg_iter) ? 0 : -EFAULT;
 }
 
-/* Designate sk as UDP-Lite socket */
-static inline int udplite_sk_init(struct sock *sk)
-{
-	udp_init_sock(sk);
-	udp_sk(sk)->pcflag = UDPLITE_BIT;
-	return 0;
-}
-
 /*
  * 	Checksumming routines
  */

net/ipv4/udp.c

···
 }
 EXPORT_SYMBOL_GPL(__udp_enqueue_schedule_skb);
 
-void udp_destruct_sock(struct sock *sk)
+void udp_destruct_common(struct sock *sk)
 {
 	/* reclaim completely the forward allocated memory */
 	struct udp_sock *up = udp_sk(sk);
···
 		kfree_skb(skb);
 	}
 	udp_rmem_release(sk, total, 0, true);
+}
+EXPORT_SYMBOL_GPL(udp_destruct_common);
 
+static void udp_destruct_sock(struct sock *sk)
+{
+	udp_destruct_common(sk);
 	inet_sock_destruct(sk);
 }
-EXPORT_SYMBOL_GPL(udp_destruct_sock);
 
 int udp_init_sock(struct sock *sk)
 {
···
 	sk->sk_destruct = udp_destruct_sock;
 	return 0;
 }
-EXPORT_SYMBOL_GPL(udp_init_sock);
 
 void skb_consume_udp(struct sock *sk, struct sk_buff *skb, int len)
 {

net/ipv4/udplite.c

···
 struct udp_table 	udplite_table __read_mostly;
 EXPORT_SYMBOL(udplite_table);
 
+/* Designate sk as UDP-Lite socket */
+static int udplite_sk_init(struct sock *sk)
+{
+	udp_init_sock(sk);
+	udp_sk(sk)->pcflag = UDPLITE_BIT;
+	return 0;
+}
+
 static int udplite_rcv(struct sk_buff *skb)
 {
 	return __udp4_lib_rcv(skb, &udplite_table, IPPROTO_UDPLITE);

net/ipv6/af_inet6.c

···
 	return (struct ipv6_pinfo *)(((u8 *)sk) + offset);
 }
 
+void inet6_sock_destruct(struct sock *sk)
+{
+	inet6_cleanup_sock(sk);
+	inet_sock_destruct(sk);
+}
+
 static int inet6_create(struct net *net, struct socket *sock, int protocol,
 			int kern)
 {
···
 			inet->hdrincl = 1;
 	}
 
-	sk->sk_destruct		= inet_sock_destruct;
+	sk->sk_destruct		= inet6_sock_destruct;
 	sk->sk_family		= PF_INET6;
 	sk->sk_protocol		= protocol;
 

net/ipv6/udp.c

···
 #include <trace/events/skb.h>
 #include "udp_impl.h"
 
+static void udpv6_destruct_sock(struct sock *sk)
+{
+	udp_destruct_common(sk);
+	inet6_sock_destruct(sk);
+}
+
+int udpv6_init_sock(struct sock *sk)
+{
+	skb_queue_head_init(&udp_sk(sk)->reader_queue);
+	sk->sk_destruct = udpv6_destruct_sock;
+	return 0;
+}
+
 static u32 udp6_ehashfn(const struct net *net,
 			const struct in6_addr *laddr,
 			const u16 lport,
···
 	.connect		= ip6_datagram_connect,
 	.disconnect		= udp_disconnect,
 	.ioctl			= udp_ioctl,
-	.init			= udp_init_sock,
+	.init			= udpv6_init_sock,
 	.destroy		= udpv6_destroy_sock,
 	.setsockopt		= udpv6_setsockopt,
 	.getsockopt		= udpv6_getsockopt,

net/ipv6/udp_impl.h

···
 int __udp6_lib_err(struct sk_buff *, struct inet6_skb_parm *, u8, u8, int,
 		   __be32, struct udp_table *);
 
+int udpv6_init_sock(struct sock *sk);
 int udp_v6_get_port(struct sock *sk, unsigned short snum);
 void udp_v6_rehash(struct sock *sk);
 

net/ipv6/udplite.c

···
 #include <linux/proc_fs.h>
 #include "udp_impl.h"
 
+static int udplitev6_sk_init(struct sock *sk)
+{
+	udpv6_init_sock(sk);
+	udp_sk(sk)->pcflag = UDPLITE_BIT;
+	return 0;
+}
+
 static int udplitev6_rcv(struct sk_buff *skb)
 {
 	return __udp6_lib_rcv(skb, &udplite_table, IPPROTO_UDPLITE);
···
 	.connect	   = ip6_datagram_connect,
 	.disconnect	   = udp_disconnect,
 	.ioctl		   = udp_ioctl,
-	.init		   = udplite_sk_init,
+	.init		   = udplitev6_sk_init,
 	.destroy	   = udpv6_destroy_sock,
 	.setsockopt	   = udpv6_setsockopt,
 	.getsockopt	   = udpv6_getsockopt,