[PATCH v2] wifi: wilc1000: avoid buffer overflow in WID string configuration

[<Ajay.Kathat@xxxxxxxxxxxxx>]

Fix the following copy overflow warning identified by Smatch checker.

 drivers/net/wireless/microchip/wilc1000/wlan_cfg.c:184 wilc_wlan_parse_response_frame()
        error: '__memcpy()' 'cfg->s[i]->str' copy overflow (512 vs 65537)

This patch introduces size check before accessing the memory buffer.
The checks are base on the WID type of received data from the firmware.
For WID string configuration, the size limit is determined by individual
element size in 'struct wilc_cfg_str_vals' that is maintained in 'len' field
of 'struct wilc_cfg_str'.

Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Closes: https://lore.kernel.org/linux-wireless/aLFbr9Yu9j_TQTey@stanley.mountain
Suggested-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Ajay Singh <ajay.kathat@xxxxxxxxxxxxx>
---

v2:
 - change the limit check for WID string
 - use even sizes for WID string buffers

---
 .../wireless/microchip/wilc1000/wlan_cfg.c    | 37 ++++++++++++++-----
 .../wireless/microchip/wilc1000/wlan_cfg.h    |  5 ++-
 2 files changed, 30 insertions(+), 12 deletions(-)

diff --git a/drivers/net/wireless/microchip/wilc1000/wlan_cfg.c b/drivers/net/wireless/microchip/wilc1000/wlan_cfg.c
index 131388886acb..cfabd5aebb54 100644
--- a/drivers/net/wireless/microchip/wilc1000/wlan_cfg.c
+++ b/drivers/net/wireless/microchip/wilc1000/wlan_cfg.c
@@ -41,10 +41,10 @@ static const struct wilc_cfg_word g_cfg_word[] = {
 };

 static const struct wilc_cfg_str g_cfg_str[] = {
-	{WID_FIRMWARE_VERSION, NULL},
-	{WID_MAC_ADDR, NULL},
-	{WID_ASSOC_RES_INFO, NULL},
-	{WID_NIL, NULL}
+	{WID_FIRMWARE_VERSION, 0, NULL},
+	{WID_MAC_ADDR, 0, NULL},
+	{WID_ASSOC_RES_INFO, 0, NULL},
+	{WID_NIL, 0, NULL}
 };

 #define WILC_RESP_MSG_TYPE_CONFIG_REPLY		'R'
@@ -147,44 +147,58 @@ static void wilc_wlan_parse_response_frame(struct wilc *wl, u8 *info, int size)

 		switch (FIELD_GET(WILC_WID_TYPE, wid)) {
 		case WID_CHAR:
+			len = 3;
+			if (len + 2  > size)
+				return;
+
 			while (cfg->b[i].id != WID_NIL && cfg->b[i].id != wid)
 				i++;

 			if (cfg->b[i].id == wid)
 				cfg->b[i].val = info[4];

-			len = 3;
 			break;

 		case WID_SHORT:
+			len = 4;
+			if (len + 2  > size)
+				return;
+
 			while (cfg->hw[i].id != WID_NIL && cfg->hw[i].id != wid)
 				i++;

 			if (cfg->hw[i].id == wid)
 				cfg->hw[i].val = get_unaligned_le16(&info[4]);

-			len = 4;
 			break;

 		case WID_INT:
+			len = 6;
+			if (len + 2  > size)
+				return;
+
 			while (cfg->w[i].id != WID_NIL && cfg->w[i].id != wid)
 				i++;

 			if (cfg->w[i].id == wid)
 				cfg->w[i].val = get_unaligned_le32(&info[4]);

-			len = 6;
 			break;

 		case WID_STR:
+			len = 2 + get_unaligned_le16(&info[2]);
+
 			while (cfg->s[i].id != WID_NIL && cfg->s[i].id != wid)
 				i++;

-			if (cfg->s[i].id == wid)
+			if (cfg->s[i].id == wid) {
+				if (len > cfg->s[i].len || (len + 2  > size))
+					return;
+
 				memcpy(cfg->s[i].str, &info[2],
-				       get_unaligned_le16(&info[2]) + 2);
+				       len);
+			}

-			len = 2 + get_unaligned_le16(&info[2]);
 			break;

 		default:
@@ -384,12 +398,15 @@ int wilc_wlan_cfg_init(struct wilc *wl)
 	/* store the string cfg parameters */
 	wl->cfg.s[i].id = WID_FIRMWARE_VERSION;
 	wl->cfg.s[i].str = str_vals->firmware_version;
+	wl->cfg.s[i].len = sizeof(str_vals->firmware_version);
 	i++;
 	wl->cfg.s[i].id = WID_MAC_ADDR;
 	wl->cfg.s[i].str = str_vals->mac_address;
+	wl->cfg.s[i].len = sizeof(str_vals->mac_address);
 	i++;
 	wl->cfg.s[i].id = WID_ASSOC_RES_INFO;
 	wl->cfg.s[i].str = str_vals->assoc_rsp;
+	wl->cfg.s[i].len = sizeof(str_vals->assoc_rsp);
 	i++;
 	wl->cfg.s[i].id = WID_NIL;
 	wl->cfg.s[i].str = NULL;
diff --git a/drivers/net/wireless/microchip/wilc1000/wlan_cfg.h b/drivers/net/wireless/microchip/wilc1000/wlan_cfg.h
index 7038b74f8e8f..5ae74bced7d7 100644
--- a/drivers/net/wireless/microchip/wilc1000/wlan_cfg.h
+++ b/drivers/net/wireless/microchip/wilc1000/wlan_cfg.h
@@ -24,12 +24,13 @@ struct wilc_cfg_word {

 struct wilc_cfg_str {
 	u16 id;
+	u16 len;
 	u8 *str;
 };

 struct wilc_cfg_str_vals {
-	u8 mac_address[7];
-	u8 firmware_version[129];
+	u8 mac_address[8];
+	u8 firmware_version[130];
 	u8 assoc_rsp[WILC_MAX_ASSOC_RESP_FRAME_SIZE];
 };

--
2.34.1