mac80211: Use memset_after() to clear tx status

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.

Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Christian Lamparter <chunkeey@gmail.com> [both CARL9170+P54USB on real HW]
Link: https://lore.kernel.org/r/20211118203839.1289276-1-keescook@chromium.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/drivers/net/wireless/ath/carl9170/tx.c b/drivers/net/wireless/ath/carl9170/tx.c
index 88444fe..1b76f44 100644 (file)
--- a/drivers/net/wireless/ath/carl9170/tx.c
+++ b/drivers/net/wireless/ath/carl9170/tx.c
@@ -275,12 +275,12 @@ 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));
+       /*
+        * This does not call ieee80211_tx_info_clear_status() because
+        * carl9170_tx_fill_rateinfo() has filled the rate information
+        * before we get to this point.
+        */
+       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 873fea5..8414aa2 100644 (file)
--- 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 10e6fe2..e349f57 100644 (file)
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -1205,12 +1205,7 @@ 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);
 }