[PATCH for-next 12/25] cm4000_cs: Use struct_group() to zero struct cm4000_dev 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 region of struct cm4000_dev that should be
initialized to zero.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/lkml/YQDvxAofJlI1JoGZ@xxxxxxxxx
---
 drivers/char/pcmcia/cm4000_cs.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/char/pcmcia/cm4000_cs.c b/drivers/char/pcmcia/cm4000_cs.c
index 8f1bce0b4fe5..adaec8fd4b16 100644
--- a/drivers/char/pcmcia/cm4000_cs.c
+++ b/drivers/char/pcmcia/cm4000_cs.c
@@ -116,8 +116,9 @@ struct cm4000_dev {
 	wait_queue_head_t atrq;		/* wait for ATR valid */
 	wait_queue_head_t readq;	/* used by write to wake blk.read */
 
-	/* warning: do not move this fields.
+	/* warning: do not move this struct group.
 	 * initialising to zero depends on it - see ZERO_DEV below.  */
+	struct_group(init,
 	unsigned char atr_csum;
 	unsigned char atr_len_retry;
 	unsigned short atr_len;
@@ -140,12 +141,10 @@ struct cm4000_dev {
 
 	struct timer_list timer;	/* used to keep monitor running */
 	int monitor_running;
+	);
 };
 
-#define	ZERO_DEV(dev)  						\
-	memset(&dev->atr_csum,0,				\
-		sizeof(struct cm4000_dev) - 			\
-		offsetof(struct cm4000_dev, atr_csum))
+#define	ZERO_DEV(dev)	memset(&((dev)->init), 0, sizeof((dev)->init))
 
 static struct pcmcia_device *dev_table[CM4000_MAX_DEV];
 static struct class *cmm_class;
-- 
2.30.2