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

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Date:   Tue, 22 Feb 2022 20:39:11 -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 6/6][next] ath6kl: wmi: Replace one-element array with
 flexible-array  member in struct wmi_aplist_event

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

It's also worth noting that due to the flexible array transformation,
the size of struct wmi_aplist_event changed (now the size is 8-byte
smaller), and in order to preserve the logic of before the transformation,
the following change is needed:

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

sizeof(struct wmi_aplist_event) before the flex-array transformation:

struct wmi_aplist_event {
	u8                         ap_list_ver;          /*     0     1 */
	u8                         num_ap;               /*     1     1 */
	union wmi_ap_info          ap_list[1];           /*     2     8 */

	/* size: 10, cachelines: 1, members: 3 */
	/* last cacheline: 10 bytes */
};

sizeof(struct wmi_aplist_event) after the flex-array transformation:

struct wmi_aplist_event {
	u8                         ap_list_ver;          /*     0     1 */
	u8                         num_ap;               /*     1     1 */
	union wmi_ap_info          ap_list[];            /*     2     0 */

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

Also, make use of the struct_size() helper and remove unneeded variable
ap_info_entry_size.

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_aplist_event))
        +       if (len <= sizeof(struct wmi_aplist_event))

Thanks

 drivers/net/wireless/ath/ath6kl/wmi.c | 7 ++-----
 drivers/net/wireless/ath/ath6kl/wmi.h | 2 +-
 2 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/net/wireless/ath/ath6kl/wmi.c b/drivers/net/wireless/ath/ath6kl/wmi.c
index 645fb6cae3be..484d37e66ce6 100644
--- a/drivers/net/wireless/ath/ath6kl/wmi.c
+++ b/drivers/net/wireless/ath/ath6kl/wmi.c
@@ -1750,23 +1750,20 @@ static int ath6kl_wmi_snr_threshold_event_rx(struct wmi *wmi, u8 *datap,
 
 static int ath6kl_wmi_aplist_event_rx(struct wmi *wmi, u8 *datap, int len)
 {
-	u16 ap_info_entry_size;
 	struct wmi_aplist_event *ev = (struct wmi_aplist_event *) datap;
 	struct wmi_ap_info_v1 *ap_info_v1;
 	u8 index;
 
-	if (len < sizeof(struct wmi_aplist_event) ||
+	if (len <= sizeof(struct wmi_aplist_event) ||
 	    ev->ap_list_ver != APLIST_VER1)
 		return -EINVAL;
 
-	ap_info_entry_size = sizeof(struct wmi_ap_info_v1);
 	ap_info_v1 = (struct wmi_ap_info_v1 *) ev->ap_list;
 
 	ath6kl_dbg(ATH6KL_DBG_WMI,
 		   "number of APs in aplist event: %d\n", ev->num_ap);
 
-	if (len < (int) (sizeof(struct wmi_aplist_event) +
-			 (ev->num_ap - 1) * ap_info_entry_size))
+	if (len < struct_size(ev, ap_list, ev->num_ap))
 		return -EINVAL;
 
 	/* AP list version 1 contents */
diff --git a/drivers/net/wireless/ath/ath6kl/wmi.h b/drivers/net/wireless/ath/ath6kl/wmi.h
index 6a7fc07cd9aa..a9732660192a 100644
--- a/drivers/net/wireless/ath/ath6kl/wmi.h
+++ b/drivers/net/wireless/ath/ath6kl/wmi.h
@@ -1957,7 +1957,7 @@ union wmi_ap_info {
 struct wmi_aplist_event {
 	u8 ap_list_ver;
 	u8 num_ap;
-	union wmi_ap_info ap_list[1];
+	union wmi_ap_info ap_list[];
 } __packed;
 
 /* Developer Commands */
-- 
2.27.0