linux-hardening - [PATCH v2][next] wifi: wil6210: wmi: Use __counted_by() in struct wmi_set_link_monitor

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Message-ID: <ZgSTCmdP+omePvWg@neat>
Date: Wed, 27 Mar 2024 15:43:38 -0600
From: "Gustavo A. R. Silva" <gustavoars@...nel.org>
To: Kalle Valo <kvalo@...nel.org>, Jeff Johnson <quic_jjohnson@...cinc.com>
Cc: linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	linux-hardening@...r.kernel.org
Subject: [PATCH v2][next] wifi: wil6210: wmi: Use __counted_by() in struct
 wmi_set_link_monitor_cmd and avoid -Wfamnae warning

Prepare for the coming implementation by GCC and Clang of the
__counted_by attribute. Flexible array members annotated with
__counted_by can have their accesses bounds-checked at run-time
via CONFIG_UBSAN_BOUNDS (for array indexing) and CONFIG_FORTIFY_SOURCE
(for strcpy/memcpy-family functions).

Also, -Wflex-array-member-not-at-end is coming in GCC-14, and we are
getting ready to enable it globally.

So, use the `DEFINE_FLEX()` helper for an on-stack definition of
a flexible structure where the size of the flexible-array member
is known at compile-time, and refactor the rest of the code,
accordingly.

So, with these changes, fix the following warning:
drivers/net/wireless/ath/wil6210/wmi.c:4018:49: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Link: https://github.com/KSPP/linux/issues/202
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
Changes in v2:
 - Use __struct_size() to get the compile-time size of the flex-struct
   instance.

v1:
 - Link: https://lore.kernel.org/linux-hardening/ZgRsn72WkHzfCUsa@neat/

 drivers/net/wireless/ath/wil6210/wmi.c | 19 +++++++------------
 drivers/net/wireless/ath/wil6210/wmi.h |  2 +-
 2 files changed, 8 insertions(+), 13 deletions(-)

diff --git a/drivers/net/wireless/ath/wil6210/wmi.c b/drivers/net/wireless/ath/wil6210/wmi.c
index 6fdb77d4c59e..8ff69dc72fb9 100644
--- a/drivers/net/wireless/ath/wil6210/wmi.c
+++ b/drivers/net/wireless/ath/wil6210/wmi.c
@@ -4014,28 +4014,23 @@ int wmi_set_cqm_rssi_config(struct wil6210_priv *wil,
 	struct net_device *ndev = wil->main_ndev;
 	struct wil6210_vif *vif = ndev_to_vif(ndev);
 	int rc;
-	struct {
-		struct wmi_set_link_monitor_cmd cmd;
-		s8 rssi_thold;
-	} __packed cmd = {
-		.cmd = {
-			.rssi_hyst = rssi_hyst,
-			.rssi_thresholds_list_size = 1,
-		},
-		.rssi_thold = rssi_thold,
-	};
 	struct {
 		struct wmi_cmd_hdr hdr;
 		struct wmi_set_link_monitor_event evt;
 	} __packed reply = {
 		.evt = {.status = WMI_FW_STATUS_FAILURE},
 	};
+	DEFINE_FLEX(struct wmi_set_link_monitor_cmd, cmd,
+		    rssi_thresholds_list, rssi_thresholds_list_size, 1);
+
+	cmd->rssi_hyst = rssi_hyst;
+	cmd->rssi_thresholds_list[0] = rssi_thold;
 
 	if (rssi_thold > S8_MAX || rssi_thold < S8_MIN || rssi_hyst > U8_MAX)
 		return -EINVAL;
 
-	rc = wmi_call(wil, WMI_SET_LINK_MONITOR_CMDID, vif->mid, &cmd,
-		      sizeof(cmd), WMI_SET_LINK_MONITOR_EVENTID,
+	rc = wmi_call(wil, WMI_SET_LINK_MONITOR_CMDID, vif->mid, cmd,
+		      __struct_size(cmd), WMI_SET_LINK_MONITOR_EVENTID,
 		      &reply, sizeof(reply), WIL_WMI_CALL_GENERAL_TO_MS);
 	if (rc) {
 		wil_err(wil, "WMI_SET_LINK_MONITOR_CMDID failed, rc %d\n", rc);
diff --git a/drivers/net/wireless/ath/wil6210/wmi.h b/drivers/net/wireless/ath/wil6210/wmi.h
index b47606d9068c..38f64524019e 100644
--- a/drivers/net/wireless/ath/wil6210/wmi.h
+++ b/drivers/net/wireless/ath/wil6210/wmi.h
@@ -3320,7 +3320,7 @@ struct wmi_set_link_monitor_cmd {
 	u8 rssi_hyst;
 	u8 reserved[12];
 	u8 rssi_thresholds_list_size;
-	s8 rssi_thresholds_list[];
+	s8 rssi_thresholds_list[] __counted_by(rssi_thresholds_list_size);
 } __packed;
 
 /* wmi_link_monitor_event_type */
-- 
2.34.1