[PATCH v2] intersil: Use struct_group() for memcpy() region

[Kees Cook]

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

Use struct_group() in struct hfa384x_tx_frame around members
frame_control, duration_id, addr1, addr2, addr3, and seq_ctrl, so they
can be referenced together. This will allow memcpy() and sizeof() to
more easily reason about sizes, improve readability, and avoid future
warnings about writing beyond the end of frame_control.

"pahole" shows no size nor member offset changes to struct
hfa384x_tx_frame. "objdump -d" shows no object code changes.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
v1->v2: rename "frame" to "header"
---
 drivers/net/wireless/intersil/hostap/hostap_hw.c   |  5 +++--
 drivers/net/wireless/intersil/hostap/hostap_wlan.h | 14 ++++++++------
 2 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/net/wireless/intersil/hostap/hostap_hw.c b/drivers/net/wireless/intersil/hostap/hostap_hw.c
index e459e7192ae9..b74f4cb5d6d3 100644
--- a/drivers/net/wireless/intersil/hostap/hostap_hw.c
+++ b/drivers/net/wireless/intersil/hostap/hostap_hw.c
@@ -1815,8 +1815,9 @@ static int prism2_tx_80211(struct sk_buff *skb, struct net_device *dev)
 	memset(&txdesc, 0, sizeof(txdesc));
 
 	/* skb->data starts with txdesc->frame_control */
-	hdr_len = 24;
-	skb_copy_from_linear_data(skb, &txdesc.frame_control, hdr_len);
+	hdr_len = sizeof(txdesc.header);
+	BUILD_BUG_ON(hdr_len != 24);
+	skb_copy_from_linear_data(skb, &txdesc.header, hdr_len);
 	if (ieee80211_is_data(txdesc.frame_control) &&
 	    ieee80211_has_a4(txdesc.frame_control) &&
 	    skb->len >= 30) {
diff --git a/drivers/net/wireless/intersil/hostap/hostap_wlan.h b/drivers/net/wireless/intersil/hostap/hostap_wlan.h
index dd2603d9b5d3..c25cd21d18bd 100644
--- a/drivers/net/wireless/intersil/hostap/hostap_wlan.h
+++ b/drivers/net/wireless/intersil/hostap/hostap_wlan.h
@@ -115,12 +115,14 @@ struct hfa384x_tx_frame {
 	__le16 tx_control; /* HFA384X_TX_CTRL_ flags */
 
 	/* 802.11 */
-	__le16 frame_control; /* parts not used */
-	__le16 duration_id;
-	u8 addr1[ETH_ALEN];
-	u8 addr2[ETH_ALEN]; /* filled by firmware */
-	u8 addr3[ETH_ALEN];
-	__le16 seq_ctrl; /* filled by firmware */
+	struct_group(header,
+		__le16 frame_control; /* parts not used */
+		__le16 duration_id;
+		u8 addr1[ETH_ALEN];
+		u8 addr2[ETH_ALEN]; /* filled by firmware */
+		u8 addr3[ETH_ALEN];
+		__le16 seq_ctrl; /* filled by firmware */
+	);
 	u8 addr4[ETH_ALEN];
 	__le16 data_len;
 
-- 
2.30.2