linux-kernel - [PATCH AUTOSEL 4.14 2/8] wifi: mwifiex: fix fortify warning

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Message-Id: <20230908182127.3461199-2-sashal@kernel.org>
Date:   Fri,  8 Sep 2023 14:21:21 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Dmitry Antipov <dmantipov@...dex.ru>,
        Brian Norris <briannorris@...omium.org>,
        Kalle Valo <kvalo@...nel.org>, Sasha Levin <sashal@...nel.org>,
        linux-wireless@...r.kernel.org
Subject: [PATCH AUTOSEL 4.14 2/8] wifi: mwifiex: fix fortify warning

From: Dmitry Antipov <dmantipov@...dex.ru>

[ Upstream commit dcce94b80a954a8968ff29fafcfb066d6197fa9a ]

When compiling with gcc 13.1 and CONFIG_FORTIFY_SOURCE=y,
I've noticed the following:

In function ‘fortify_memcpy_chk’,
    inlined from ‘mwifiex_construct_tdls_action_frame’ at drivers/net/wireless/marvell/mwifiex/tdls.c:765:3,
    inlined from ‘mwifiex_send_tdls_action_frame’ at drivers/net/wireless/marvell/mwifiex/tdls.c:856:6:
./include/linux/fortify-string.h:529:25: warning: call to ‘__read_overflow2_field’
declared with attribute warning: detected read beyond size of field (2nd parameter);
maybe use struct_group()? [-Wattribute-warning]
  529 |                         __read_overflow2_field(q_size_field, size);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The compiler actually complains on:

memmove(pos + ETH_ALEN, &mgmt->u.action.category,
	sizeof(mgmt->u.action.u.tdls_discover_resp));

and it happens because the fortification logic interprets this
as an attempt to overread 1-byte 'u.action.category' member of
'struct ieee80211_mgmt'. To silence this warning, it's enough
to pass an address of 'u.action' itself instead of an address
of its first member.

This also fixes an improper usage of 'sizeof()'. Since 'skb' is
extended with 'sizeof(mgmt->u.action.u.tdls_discover_resp) + 1'
bytes (where 1 is actually 'sizeof(mgmt->u.action.category)'),
I assume that the same number of bytes should be copied.

Suggested-by: Brian Norris <briannorris@...omium.org>
Signed-off-by: Dmitry Antipov <dmantipov@...dex.ru>
Reviewed-by: Brian Norris <briannorris@...omium.org>
Signed-off-by: Kalle Valo <kvalo@...nel.org>
Link: https://lore.kernel.org/r/20230629085115.180499-2-dmantipov@yandex.ru
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/net/wireless/marvell/mwifiex/tdls.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/net/wireless/marvell/mwifiex/tdls.c b/drivers/net/wireless/marvell/mwifiex/tdls.c
index 80d20fb6f3480..a69b4983747f3 100644
--- a/drivers/net/wireless/marvell/mwifiex/tdls.c
+++ b/drivers/net/wireless/marvell/mwifiex/tdls.c
@@ -737,6 +737,7 @@ mwifiex_construct_tdls_action_frame(struct mwifiex_private *priv,
 	int ret;
 	u16 capab;
 	struct ieee80211_ht_cap *ht_cap;
+	unsigned int extra;
 	u8 radio, *pos;
 
 	capab = priv->curr_bss_params.bss_descriptor.cap_info_bitmap;
@@ -755,7 +756,10 @@ mwifiex_construct_tdls_action_frame(struct mwifiex_private *priv,
 
 	switch (action_code) {
 	case WLAN_PUB_ACTION_TDLS_DISCOVER_RES:
-		skb_put(skb, sizeof(mgmt->u.action.u.tdls_discover_resp) + 1);
+		/* See the layout of 'struct ieee80211_mgmt'. */
+		extra = sizeof(mgmt->u.action.u.tdls_discover_resp) +
+			sizeof(mgmt->u.action.category);
+		skb_put(skb, extra);
 		mgmt->u.action.category = WLAN_CATEGORY_PUBLIC;
 		mgmt->u.action.u.tdls_discover_resp.action_code =
 					      WLAN_PUB_ACTION_TDLS_DISCOVER_RES;
@@ -764,8 +768,7 @@ mwifiex_construct_tdls_action_frame(struct mwifiex_private *priv,
 		mgmt->u.action.u.tdls_discover_resp.capability =
 							     cpu_to_le16(capab);
 		/* move back for addr4 */
-		memmove(pos + ETH_ALEN, &mgmt->u.action.category,
-			sizeof(mgmt->u.action.u.tdls_discover_resp));
+		memmove(pos + ETH_ALEN, &mgmt->u.action, extra);
 		/* init address 4 */
 		memcpy(pos, bc_addr, ETH_ALEN);
 
-- 
2.40.1