[PATCH 39/64] mac80211: Use memset_after() to clear tx status

[Kees Cook]

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

Use memset_after() so memset() doesn't get confused about writing
beyond the destination member that is intended to be the starting point
of zeroing through the end of the struct.

Note that the common helper, ieee80211_tx_info_clear_status(), does NOT
clear ack_signal, but the open-coded versions do. All three perform
checks that the ack_signal position hasn't changed, though.

Signed-off-by: Kees Cook <keesc...@chromium.org>
---
Should these each be clearing the same region? Because they're currently not.
---
 drivers/net/wireless/ath/carl9170/tx.c   | 4 +---
 drivers/net/wireless/intersil/p54/txrx.c | 4 +---
 include/net/mac80211.h                   | 4 +---
 3 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/drivers/net/wireless/ath/carl9170/tx.c 
b/drivers/net/wireless/ath/carl9170/tx.c
index 88444fe6d1c6..6d2115639434 100644
--- a/drivers/net/wireless/ath/carl9170/tx.c
+++ b/drivers/net/wireless/ath/carl9170/tx.c
@@ -278,9 +278,7 @@ static void carl9170_tx_release(struct kref *ref)
        BUILD_BUG_ON(
            offsetof(struct ieee80211_tx_info, status.ack_signal) != 20);
 
-       memset(&txinfo->status.ack_signal, 0,
-              sizeof(struct ieee80211_tx_info) -
-              offsetof(struct ieee80211_tx_info, status.ack_signal));
+       memset_after(&txinfo->status, 0, rates);
 
        if (atomic_read(&ar->tx_total_queued))
                ar->tx_schedule = true;
diff --git a/drivers/net/wireless/intersil/p54/txrx.c 
b/drivers/net/wireless/intersil/p54/txrx.c
index 873fea59894f..f71b355f8583 100644
--- a/drivers/net/wireless/intersil/p54/txrx.c
+++ b/drivers/net/wireless/intersil/p54/txrx.c
@@ -431,9 +431,7 @@ static void p54_rx_frame_sent(struct p54_common *priv, 
struct sk_buff *skb)
         * Clear manually, ieee80211_tx_info_clear_status would
         * clear the counts too and we need them.
         */
-       memset(&info->status.ack_signal, 0,
-              sizeof(struct ieee80211_tx_info) -
-              offsetof(struct ieee80211_tx_info, status.ack_signal));
+       memset_after(&info->status, 0, rates);
        BUILD_BUG_ON(offsetof(struct ieee80211_tx_info,
                              status.ack_signal) != 20);
 
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index d8a1d09a2141..7abc1427aa8c 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -1200,9 +1200,7 @@ ieee80211_tx_info_clear_status(struct ieee80211_tx_info 
*info)
 
        BUILD_BUG_ON(
            offsetof(struct ieee80211_tx_info, status.ack_signal) != 20);
-       memset(&info->status.ampdu_ack_len, 0,
-              sizeof(struct ieee80211_tx_info) -
-              offsetof(struct ieee80211_tx_info, status.ampdu_ack_len));
+       memset_after(&info->status, 0, ack_signal);
 }
 
 
-- 
2.30.2