wifi: carl9170: re-fix fortified-memset warning

[ Upstream commit 066afaf ]

The carl9170_tx_release() function sometimes triggers a fortified-memset
warning in my randconfig builds:

In file included from include/linux/string.h:254,
                 from drivers/net/wireless/ath/carl9170/tx.c:40:
In function 'fortify_memset_chk',
    inlined from 'carl9170_tx_release' at drivers/net/wireless/ath/carl9170/tx.c:283:2,
    inlined from 'kref_put' at include/linux/kref.h:65:3,
    inlined from 'carl9170_tx_put_skb' at drivers/net/wireless/ath/carl9170/tx.c:342:9:
include/linux/fortify-string.h:493:25: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
  493 |                         __write_overflow_field(p_size_field, size);

Kees previously tried to avoid this by using memset_after(), but it seems
this does not fully address the problem. I noticed that the memset_after()
here is done on a different part of the union (status) than the original
cast was from (rate_driver_data), which may confuse the compiler.

Unfortunately, the memset_after() trick does not work on driver_rates[]
because that is part of an anonymous struct, and I could not get
struct_group() to do this either. Using two separate memset() calls
on the two members does address the warning though.

Fixes: fb5f6a0 ("mac80211: Use memset_after() to clear tx status")
Link: https://lore.kernel.org/lkml/[email protected]/
Signed-off-by: Arnd Bergmann <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Acked-by: Christian Lamparter <[email protected]>
Signed-off-by: Kalle Valo <[email protected]>
Link: https://msgid.link/[email protected]
Signed-off-by: Sasha Levin <[email protected]>

Author: arndb

drivers/net/wireless/ath/carl9170/tx.c

@@ -280,7 +280,8 @@ static void carl9170_tx_release(struct kref *ref)
 	 * carl9170_tx_fill_rateinfo() has filled the rate information
 	 * before we get to this point.
 	 */
-	memset_after(&txinfo->status, 0, rates);
+	memset(&txinfo->pad, 0, sizeof(txinfo->pad));
+	memset(&txinfo->rate_driver_data, 0, sizeof(txinfo->rate_driver_data));
 
 	if (atomic_read(&ar->tx_total_queued))
 		ar->tx_schedule = true;