wifi: wilc1000: validate number of channels

There is no validation of 'e->no_of_channels' which can trigger an
out-of-bounds write in the following 'memset' call. Validate that the
number of channels does not extends beyond the size of the channel list
element.
Signed-off-by: Phil Turnbull <philipturnbull@github.com>
Tested-by: Ajay Kathat <ajay.kathat@microchip.com>
Acked-by: Ajay Kathat <ajay.kathat@microchip.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20221123153543.8568-5-philipturnbull@github.com

drivers/net/wireless/microchip/wilc1000/cfg80211.c

@@ -981,19 +981,29 @@ static inline void wilc_wfi_cfg_parse_ch_attr(u8 *buf, u32 len, u8 sta_ch)
 	}
 
 	if (ch_list_idx) {
-		u16 attr_size;
-		struct wilc_ch_list_elem *e;
-		int i;
+		u16 elem_size;
 
 		ch_list = (struct wilc_attr_ch_list *)&buf[ch_list_idx];
-		attr_size = le16_to_cpu(ch_list->attr_len);
-		for (i = 0; i < attr_size;) {
+		/* the number of bytes following the final 'elem' member */
+		elem_size = le16_to_cpu(ch_list->attr_len) -
+			(sizeof(*ch_list) - sizeof(struct wilc_attr_entry));
+		for (unsigned int i = 0; i < elem_size;) {
+			struct wilc_ch_list_elem *e;
+
 			e = (struct wilc_ch_list_elem *)(ch_list->elem + i);
+
+			i += sizeof(*e);
+			if (i > elem_size)
+				break;
+
+			i += e->no_of_channels;
+			if (i > elem_size)
+				break;
+
 			if (e->op_class == WILC_WLAN_OPERATING_CLASS_2_4GHZ) {
 				memset(e->ch_list, sta_ch, e->no_of_channels);
 				break;
 			}
-			i += e->no_of_channels;
 		}
 	}