[PATCH v2 60/63] net/af_iucv: Use struct_group() to zero struct iucv_sock region

[Kees Cook]

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Add struct_group() to mark the region of struct iucv_sock that gets
initialized to zero. Avoid the future warning:

In function 'fortify_memset_chk',
    inlined from 'iucv_sock_alloc' at net/iucv/af_iucv.c:476:2:
./include/linux/fortify-string.h:199:4: warning: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Wattribute-warning]
  199 |    __write_overflow_field(p_size_field, size);
      |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Cc: Julian Wiedmann <jwi@xxxxxxxxxxxxx>
Cc: Karsten Graul <kgraul@xxxxxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: linux-s390@xxxxxxxxxxxxxxx
Cc: netdev@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 include/net/iucv/af_iucv.h | 10 ++++++----
 net/iucv/af_iucv.c         |  2 +-
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/net/iucv/af_iucv.h b/include/net/iucv/af_iucv.h
index ff06246dbbb9..df85d19fbf84 100644
--- a/include/net/iucv/af_iucv.h
+++ b/include/net/iucv/af_iucv.h
@@ -112,10 +112,12 @@ enum iucv_tx_notify {
 
 struct iucv_sock {
 	struct sock		sk;
-	char			src_user_id[8];
-	char			src_name[8];
-	char			dst_user_id[8];
-	char			dst_name[8];
+	struct_group(init,
+		char		src_user_id[8];
+		char		src_name[8];
+		char		dst_user_id[8];
+		char		dst_name[8];
+	);
 	struct list_head	accept_q;
 	spinlock_t		accept_q_lock;
 	struct sock		*parent;
diff --git a/net/iucv/af_iucv.c b/net/iucv/af_iucv.c
index 18316ee3c692..9446e2771d31 100644
--- a/net/iucv/af_iucv.c
+++ b/net/iucv/af_iucv.c
@@ -473,7 +473,7 @@ static struct sock *iucv_sock_alloc(struct socket *sock, int proto, gfp_t prio,
 	atomic_set(&iucv->msg_recv, 0);
 	iucv->path = NULL;
 	iucv->sk_txnotify = afiucv_hs_callback_txnotify;
-	memset(&iucv->src_user_id , 0, 32);
+	memset(&iucv->init, 0, sizeof(iucv->init));
 	if (pr_iucv)
 		iucv->transport = AF_IUCV_TRANS_IUCV;
 	else
-- 
2.30.2