linux-kernel - [PATCH 3/6][next] ath6kl: wmi: Replace one-element array with flexible-array member in struct wmi_channel_list

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Date:   Tue, 22 Feb 2022 20:38:50 -0600
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Kalle Valo <kvalo@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-hardening@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Subject: [PATCH 3/6][next] ath6kl: wmi: Replace one-element array with
 flexible-array  member in struct wmi_channel_list_reply

Replace one-element array with flexible-array member in struct
wmi_channel_list_reply.

It's also worth noting that due to the flexible array transformation,
the size of struct wmi_channel_list_reply changed, see below.

Before flex-array transformation:

struct wmi_channel_list_reply {
	u8                         reserved;             /*     0     1 */
	u8                         num_ch;               /*     1     1 */
	__le16                     ch_list[1];           /*     2     2 */

	/* size: 4, cachelines: 1, members: 3 */
	/* last cacheline: 4 bytes */
};

After flex-array transformation:

struct wmi_channel_list_reply {
	u8                         reserved;             /*     0     1 */
	u8                         num_ch;               /*     1     1 */
	__le16                     ch_list[];            /*     2     0 */

	/* size: 2, cachelines: 1, members: 3 */
	/* last cacheline: 2 bytes */
};

So, the following change preserves the logic that if _len_ is at least
4 bytes in size, this is the existence of at least one channel in
ch_list[] is being considered, then the execution jumps to call
ath6kl_wakeup_event(wmi->parent_dev);, otherwise _len_ is 2 bytes or
less and the code returns -EINVAL:

	-       if (len < sizeof(struct wmi_channel_list_reply))
	+       if (len <= sizeof(struct wmi_channel_list_reply))

This issue was found with the help of Coccinelle and audited and fixed,
manually.

Link: https://www.kernel.org/doc/html/v5.16/process/deprecated.html#zero-length-and-one-element-arrays
Link: https://github.com/KSPP/linux/issues/79
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
Hi!

It'd be great if someone can confirm or comment on the following
changes described in the changelog text:

	-       if (len < sizeof(struct wmi_channel_list_reply))
	+       if (len <= sizeof(struct wmi_channel_list_reply))

Thanks

 drivers/net/wireless/ath/ath6kl/wmi.c | 2 +-
 drivers/net/wireless/ath/ath6kl/wmi.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/ath/ath6kl/wmi.c b/drivers/net/wireless/ath/ath6kl/wmi.c
index bdfc057c5a82..049d75f31f3c 100644
--- a/drivers/net/wireless/ath/ath6kl/wmi.c
+++ b/drivers/net/wireless/ath/ath6kl/wmi.c
@@ -1240,7 +1240,7 @@ static int ath6kl_wmi_ratemask_reply_rx(struct wmi *wmi, u8 *datap, int len)
 
 static int ath6kl_wmi_ch_list_reply_rx(struct wmi *wmi, u8 *datap, int len)
 {
-	if (len < sizeof(struct wmi_channel_list_reply))
+	if (len <= sizeof(struct wmi_channel_list_reply))
 		return -EINVAL;
 
 	ath6kl_wakeup_event(wmi->parent_dev);
diff --git a/drivers/net/wireless/ath/ath6kl/wmi.h b/drivers/net/wireless/ath/ath6kl/wmi.h
index 9e168752bec2..432e4f428a4a 100644
--- a/drivers/net/wireless/ath/ath6kl/wmi.h
+++ b/drivers/net/wireless/ath/ath6kl/wmi.h
@@ -1373,7 +1373,7 @@ struct wmi_channel_list_reply {
 	u8 num_ch;
 
 	/* channel in Mhz */
-	__le16 ch_list[1];
+	__le16 ch_list[];
 } __packed;
 
 /* List of Events (target to host) */
-- 
2.27.0