[PATCH v2 44/63] mac80211: Use memset_after() to clear tx status

Kees Cook
2021-08-18T06:17:05Z

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.

Additionally fix the common helper, ieee80211_tx_info_clear_status(),
which was not clearing ack_signal, but the open-coded versions
did. Johannes Berg points out this bug was introduced by commit
e3e1a0bcb3f1 ("mac80211: reduce IEEE80211_TX_MAX_RATES") but was harmless.

Also drops the associated unneeded BUILD_BUG_ON()s, and adds a note to
carl9170 about usage.

Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
drivers/net/wireless/ath/carl9170/tx.c | 11 +++++------
drivers/net/wireless/intersil/p54/txrx.c | 6 +-----
include/net/mac80211.h | 7 +------
3 files changed, 7 insertions(+), 17 deletions(-)

diff --git a/drivers/net/wireless/ath/carl9170/tx.c b/drivers/net/wireless/ath/carl9170/tx.c
index 88444fe6d1c6..aa95d1a65882 100644
--- a/drivers/net/wireless/ath/carl9170/tx.c
+++ b/drivers/net/wireless/ath/carl9170/tx.c
@@ -275,12 +275,11 @@ static void carl9170_tx_release(struct kref *ref)
if (WARN_ON_ONCE(!ar))
return;

- 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));
+ /*
+ * Should this call ieee80211_tx_info_clear_status() instead of clearing
+ * manually? txinfo->status.rates do not seem to be used here.
+ */
+ 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..8414aa208655 100644
--- a/drivers/net/wireless/intersil/p54/txrx.c
+++ b/drivers/net/wireless/intersil/p54/txrx.c
@@ -431,11 +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));
- BUILD_BUG_ON(offsetof(struct ieee80211_tx_info,
- status.ack_signal) != 20);
+ memset_after(&info->status, 0, rates);

if (entry_hdr->flags & cpu_to_le16(P54_HDR_FLAG_DATA_ALIGN))
pad = entry_data->align[0];
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index d8a1d09a2141..4c469b04de37 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -1197,12 +1197,7 @@ ieee80211_tx_info_clear_status(struct ieee80211_tx_info *info)
/* clear the rate counts */
for (i = 0; i < IEEE80211_TX_MAX_RATES; i++)
info->status.rates[i].count = 0;
-
- 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, rates);
}

--
2.30.2