prism54: potential memory corruption in prism54_get_essid()

"dwrq->length" is the capped version of "essid->length".

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/prism54/isl_ioctl.c

@@ -778,7 +778,7 @@ prism54_get_essid(struct net_device *ndev, struct iw_request_info *info,
 		dwrq->flags = 0;
 		dwrq->length = 0;
 	}
-	essid->octets[essid->length] = '\0';
+	essid->octets[dwrq->length] = '\0';
 	memcpy(extra, essid->octets, dwrq->length);
 	kfree(essid);