linux-hardening - [PATCH v2 60/63] net/af_iucv: Use struct_group() to zero struct iucv

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Date:   Tue, 17 Aug 2021 23:05:30 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-kernel@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Julian Wiedmann <jwi@...ux.ibm.com>,
        Karsten Graul <kgraul@...ux.ibm.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-s390@...r.kernel.org,
        netdev@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-wireless@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-staging@...ts.linux.dev, linux-block@...r.kernel.org,
        linux-kbuild@...r.kernel.org, clang-built-linux@...glegroups.com,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-hardening@...r.kernel.org
Subject: [PATCH v2 60/63] net/af_iucv: Use struct_group() to zero struct iucv_sock region

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@...ux.ibm.com>
Cc: Karsten Graul <kgraul@...ux.ibm.com>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Jakub Kicinski <kuba@...nel.org>
Cc: linux-s390@...r.kernel.org
Cc: netdev@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 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