net: Convert struct sockaddr to fixed-size "sa_data[14]"

Revert struct sockaddr from flexible array to fixed 14-byte "sa_data",
to solve over 36,000 -Wflex-array-member-not-at-end warnings, since
struct sockaddr is embedded within many network structs.

With socket/proto sockaddr-based internal APIs switched to use struct
sockaddr_unsized, there should be no more uses of struct sockaddr that
depend on reading beyond the end of struct sockaddr::sa_data that might
trigger bounds checking.

Comparing an x86_64 "allyesconfig" vmlinux build before and after this
patch showed no new "ud1" instructions from CONFIG_UBSAN_BOUNDS nor any
new "field-spanning" memcpy CONFIG_FORTIFY_SOURCE instrumentations.

Cc: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: Kees Cook <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

include/linux/socket.h

···
  *	1003.1g requires sa_family_t and that sa_data is char.
  */
 
+/* Deprecated for in-kernel use. Use struct sockaddr_unsized instead. */
 struct sockaddr {
 	sa_family_t	sa_family;	/* address family, AF_xxx	*/
-	union {
-		char sa_data_min[14];		/* Minimum 14 bytes of protocol address	*/
-		DECLARE_FLEX_ARRAY(char, sa_data);
-	};
+	char		sa_data[14];	/* 14 bytes of protocol address	*/
 };
 
 /**

net/core/dev.c

···
 /* "sa" is a true struct sockaddr with limited "sa_data" member. */
 int netif_get_mac_address(struct sockaddr *sa, struct net *net, char *dev_name)
 {
-	size_t size = sizeof(sa->sa_data_min);
+	size_t size = sizeof(sa->sa_data);
 	struct net_device *dev;
 	int ret = 0;
 

net/core/dev_ioctl.c

···
 		if (ifr->ifr_hwaddr.sa_family != dev->type)
 			return -EINVAL;
 		memcpy(dev->broadcast, ifr->ifr_hwaddr.sa_data,
-		       min(sizeof(ifr->ifr_hwaddr.sa_data_min),
+		       min(sizeof(ifr->ifr_hwaddr.sa_data),
 			   (size_t)dev->addr_len));
 		netdev_lock_ops(dev);
 		call_netdevice_notifiers(NETDEV_CHANGEADDR, dev);

net/ipv4/arp.c

···
 
 	read_lock_bh(&neigh->lock);
 	memcpy(r->arp_ha.sa_data, neigh->ha,
-	       min(dev->addr_len, sizeof(r->arp_ha.sa_data_min)));
+	       min(dev->addr_len, sizeof(r->arp_ha.sa_data)));
 	r->arp_flags = arp_state_to_flags(neigh);
 	read_unlock_bh(&neigh->lock);
 

net/packet/af_packet.c

···
 {
 	struct sock *sk = sock->sk;
 	struct sockaddr *sa = (struct sockaddr *)uaddr;
-	char name[sizeof(sa->sa_data_min) + 1];
+	char name[sizeof(sa->sa_data) + 1];
 
 	/*
 	 *	Check legality
···
 	/* uaddr->sa_data comes from the userspace, it's not guaranteed to be
 	 * zero-terminated.
 	 */
-	memcpy(name, sa->sa_data, sizeof(sa->sa_data_min));
-	name[sizeof(sa->sa_data_min)] = 0;
+	memcpy(name, sa->sa_data, sizeof(sa->sa_data));
+	name[sizeof(sa->sa_data)] = 0;
 
 	return packet_do_bind(sk, name, 0, 0);
 }
···
 		return -EOPNOTSUPP;
 
 	uaddr->sa_family = AF_PACKET;
-	memset(uaddr->sa_data, 0, sizeof(uaddr->sa_data_min));
+	memset(uaddr->sa_data, 0, sizeof(uaddr->sa_data));
 	rcu_read_lock();
 	dev = dev_get_by_index_rcu(sock_net(sk), READ_ONCE(pkt_sk(sk)->ifindex));
 	if (dev)
-		strscpy(uaddr->sa_data, dev->name, sizeof(uaddr->sa_data_min));
+		strscpy(uaddr->sa_data, dev->name, sizeof(uaddr->sa_data));
 	rcu_read_unlock();
 
 	return sizeof(*uaddr);

tools/perf/trace/beauty/include/linux/socket.h

···
 
 struct sockaddr {
 	sa_family_t	sa_family;	/* address family, AF_xxx	*/
-	union {
-		char sa_data_min[14];		/* Minimum 14 bytes of protocol address	*/
-		DECLARE_FLEX_ARRAY(char, sa_data);
-	};
+	char		sa_data[14];	/* 14 bytes of protocol address	*/
 };
 
 struct linger {