sock_diag: annotate data-races around sock_diag_handlers[family]

__sock_diag_cmd() and sock_diag_bind() read sock_diag_handlers[family]
without a lock held.

Use READ_ONCE()/WRITE_ONCE() annotations to avoid potential issues.

Fixes: 8ef874bfc729 ("sock_diag: Move the sock_ code to net/core/")
Signed-off-by: Eric Dumazet <[e-mail]>
Reviewed-by: Guillaume Nault <[e-mail]>
Reviewed-by: Kuniyuki Iwashima <[e-mail]>
Reviewed-by: Willem de Bruijn <[e-mail]>
Signed-off-by: Paolo Abeni <[e-mail]>

net/core/sock_diag.c

···
 	if (sock_diag_handlers[hndl->family])
 		err = -EBUSY;
 	else
-		sock_diag_handlers[hndl->family] = hndl;
+		WRITE_ONCE(sock_diag_handlers[hndl->family], hndl);
 	mutex_unlock(&sock_diag_table_mutex);
 
 	return err;
···
 
 	mutex_lock(&sock_diag_table_mutex);
 	BUG_ON(sock_diag_handlers[family] != hnld);
-	sock_diag_handlers[family] = NULL;
+	WRITE_ONCE(sock_diag_handlers[family], NULL);
 	mutex_unlock(&sock_diag_table_mutex);
 }
 EXPORT_SYMBOL_GPL(sock_diag_unregister);
···
 		return -EINVAL;
 	req->sdiag_family = array_index_nospec(req->sdiag_family, AF_MAX);
 
-	if (sock_diag_handlers[req->sdiag_family] == NULL)
+	if (READ_ONCE(sock_diag_handlers[req->sdiag_family]) == NULL)
 		sock_load_diag_module(req->sdiag_family, 0);
 
 	mutex_lock(&sock_diag_table_mutex);
···
 	switch (group) {
 	case SKNLGRP_INET_TCP_DESTROY:
 	case SKNLGRP_INET_UDP_DESTROY:
-		if (!sock_diag_handlers[AF_INET])
+		if (!READ_ONCE(sock_diag_handlers[AF_INET]))
 			sock_load_diag_module(AF_INET, 0);
 		break;
 	case SKNLGRP_INET6_TCP_DESTROY:
 	case SKNLGRP_INET6_UDP_DESTROY:
-		if (!sock_diag_handlers[AF_INET6])
+		if (!READ_ONCE(sock_diag_handlers[AF_INET6]))
 			sock_load_diag_module(AF_INET6, 0);
 		break;
 	}