staging: ks7010: potential buffer overflow in ks_wlan_set_encode_ext()

The "exc->key_len" is a u16 that comes from the user.  If it's over
IW_ENCODING_TOKEN_MAX (64) that could lead to memory corruption.

Fixes: b121d84 ("staging: ks7010: simplify calls to memcpy()")
Cc: stable <stable@kernel.org>
Signed-off-by: Zhang Shurong <zhang_shurong@foxmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/tencent_5153B668C0283CAA15AA518325346E026A09@qq.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: ZhangShurong

drivers/staging/ks7010/ks_wlan_net.c

@@ -1583,8 +1583,10 @@ static int ks_wlan_set_encode_ext(struct net_device *dev,
 			commit |= SME_WEP_FLAG;
 		}
 		if (enc->key_len) {
-			memcpy(&key->key_val[0], &enc->key[0], enc->key_len);
-			key->key_len = enc->key_len;
+			int key_len = clamp_val(enc->key_len, 0, IW_ENCODING_TOKEN_MAX);
+
+			memcpy(&key->key_val[0], &enc->key[0], key_len);
+			key->key_len = key_len;
 			commit |= (SME_WEP_VAL1 << index);
 		}
 		break;