linux-hardening - [PATCH v2][wireless-next/for-next] wifi: mt76: mt7996: Use DECLARE_FLEX

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Date: Tue, 12 Dec 2023 11:14:29 -0600
From: "Gustavo A. R. Silva" <gustavoars@...nel.org>
To: Felix Fietkau <nbd@....name>, Lorenzo Bianconi <lorenzo@...nel.org>,
	Ryder Lee <ryder.lee@...iatek.com>,
	Shayne Chen <shayne.chen@...iatek.com>,
	Sean Wang <sean.wang@...iatek.com>, Kalle Valo <kvalo@...nel.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Cc: linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	linux-hardening@...r.kernel.org
Subject: [PATCH v2][wireless-next/for-next] wifi: mt76: mt7996: Use
 DECLARE_FLEX_ARRAY() and fix -Warray-bounds warnings

Transform zero-length arrays `rate`, `adm_stat` and `msdu_cnt` into
proper flexible-array members in anonymous union in `struct
mt7996_mcu_all_sta_info_event` via the DECLARE_FLEX_ARRAY()
helper; and fix multiple -Warray-bounds warnings:

drivers/net/wireless/mediatek/mt76/mt7996/mcu.c:544:61: warning: array subscript <unknown> is outside array bounds of 'struct <anonymous>[0]' [-Warray-bounds=]
drivers/net/wireless/mediatek/mt76/mt7996/mcu.c:551:58: warning: array subscript <unknown> is outside array bounds of 'struct <anonymous>[0]' [-Warray-bounds=]
drivers/net/wireless/mediatek/mt76/mt7996/mcu.c:553:58: warning: array subscript <unknown> is outside array bounds of 'struct <anonymous>[0]' [-Warray-bounds=]
drivers/net/wireless/mediatek/mt76/mt7996/mcu.c:530:61: warning: array subscript <unknown> is outside array bounds of 'struct <anonymous>[0]' [-Warray-bounds=]
drivers/net/wireless/mediatek/mt76/mt7996/mcu.c:538:66: warning: array subscript <unknown> is outside array bounds of 'struct <anonymous>[0]' [-Warray-bounds=]
drivers/net/wireless/mediatek/mt76/mt7996/mcu.c:540:66: warning: array subscript <unknown> is outside array bounds of 'struct <anonymous>[0]' [-Warray-bounds=]
drivers/net/wireless/mediatek/mt76/mt7996/mcu.c:520:57: warning: array subscript <unknown> is outside array bounds of 'struct all_sta_trx_rate[0]' [-Warray-bounds=]
drivers/net/wireless/mediatek/mt76/mt7996/mcu.c:526:76: warning: array subscript <unknown> is outside array bounds of 'struct all_sta_trx_rate[0]' [-Warray-bounds=]
drivers/net/wireless/mediatek/mt76/mt7996/mcu.c:526:76: warning: array subscript <unknown> is outside array bounds of 'struct all_sta_trx_rate[0]' [-Warray-bounds=]
drivers/net/wireless/mediatek/mt76/mt7996/mcu.c:526:76: warning: array subscript <unknown> is outside array bounds of 'struct all_sta_trx_rate[0]' [-Warray-bounds=]
drivers/net/wireless/mediatek/mt76/mt7996/mcu.c:526:76: warning: array subscript <unknown> is outside array bounds of 'struct all_sta_trx_rate[0]' [-Warray-bounds=]

This results in no differences in binary output, helps with the ongoing
efforts to globally enable -Warray-bounds.

Reviewed-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
Changes in v2:
 - Add Kees' RB tag.
 - Transform zero-length array `rate` into flex-array member.
 - Address five more -Warray-bounds warnings introduced by fake
   flexible array `rate`

 drivers/net/wireless/mediatek/mt76/mt7996/mcu.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7996/mcu.h b/drivers/net/wireless/mediatek/mt76/mt7996/mcu.h
index 3e013b20ee5e..36cacc495c75 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7996/mcu.h
+++ b/drivers/net/wireless/mediatek/mt76/mt7996/mcu.h
@@ -206,20 +206,20 @@ struct mt7996_mcu_all_sta_info_event {
 	u8 rsv3[4];
 
 	union {
-		struct all_sta_trx_rate rate[0];
-		struct {
+		DECLARE_FLEX_ARRAY(struct all_sta_trx_rate, rate);
+		DECLARE_FLEX_ARRAY(struct {
 			__le16 wlan_idx;
 			u8 rsv[2];
 			__le32 tx_bytes[IEEE80211_NUM_ACS];
 			__le32 rx_bytes[IEEE80211_NUM_ACS];
-		} adm_stat[0] __packed;
+		} __packed, adm_stat);
 
-		struct {
+		DECLARE_FLEX_ARRAY(struct {
 			__le16 wlan_idx;
 			u8 rsv[2];
 			__le32 tx_msdu_cnt;
 			__le32 rx_msdu_cnt;
-		} msdu_cnt[0] __packed;
+		} __packed, msdu_cnt);
 	} __packed;
 } __packed;
 
-- 
2.34.1