whitelist

This is a simple whitelisting package that encompasses several common patterns into a reusable package.

The basic type of a whitelist is the ACL type, which provides a single method on a net.IP value:

• Permitted determines whether the IP address is whitelisted and therefore should be permitted access. It should return true if the address is whitelisted.

Additionally, there are two other types that are built on the ACL type; the HostACL stores individual hosts and the NetACL stores networks. Each of these provides two functions that differ in the types of their arguments.

• Add whitelists the IP address.
• Remove drops the IP address from the whitelist.

The HostACL operates on net.IP values, while the NetACL operates on *net.IPNets.

There are currently four implementations of ACL provided in this package; a basic implementation of the two types of ACLs and a stub type for each:

• Basic is a simple host-based whitelister that converts the IP addresses to strings; the whitelist is implemented as a set of string addresses. The set is implemented as a map[string]bool, and uses a sync.Mutex to coordinate updates to the whitelist.
• BasicNet is a simple network-based whitelister that similarly uses a mutex and an array to store networks. This has a number of limitations: operations are /O(n)/, and subsets/supersets of existing networks isn't detected. That is, if 192.168.3.0/24 is removed from a whitelist that has 192.168.0.0/16 permitted, that subnet will not actually be removed. Exact networks are required for Add and Remove at this time.
• HostStub and NetStub are stand-in whitelists that always permits addresses. They are vocal about logging warning messages noting that whitelisting is stubbed. They are designed to be used in cases where whitelisting is desired, but the mechanics of whitelisting (i.e. administration of the whitelist) is not yet implemented, perhaps to keep whitelists in the system's flow.

Two convenience functions are provided here for extracting IP addresses:

• NetConnLookup accepts a net.Conn value, and returns the net.IP value from the connection.
• HTTPRequestLookup accepts a *http.Request and returns the net.IP value from the request.

There are also two functions for whitelisting HTTP endpoints:

• NewHandler returns an http.Handler
• NewHandlerFunc returns an http.HandlerFunc

These endpoints will work with both HostACL and NetACL.

Example http.Handler

This is a file server that uses a pair of whitelists. The admin whitelist permits modifications to the user whitelist only by the localhost. The user whitelist controls which hosts have access to the file server.

package main

import (
	"encoding/json"
	"flag"
	"fmt"
	"log"
	"net"
	"net/http"

	"github.com/cloudflare/cfssl/whitelist"
)

var wl = whitelist.NewBasic()

func addIP(w http.ResponseWriter, r *http.Request) {
	addr := r.FormValue("ip")

	ip := net.ParseIP(addr)
	wl.Add(ip)
	log.Printf("request to add %s to the whitelist", addr)
	w.Write([]byte(fmt.Sprintf("Added %s to whitelist.\n", addr)))
}

func delIP(w http.ResponseWriter, r *http.Request) {
	addr := r.FormValue("ip")

	ip := net.ParseIP(addr)
	wl.Remove(ip)
	log.Printf("request to remove %s from the whitelist", addr)
	w.Write([]byte(fmt.Sprintf("Removed %s from whitelist.\n", ip)))
}

func dumpWhitelist(w http.ResponseWriter, r *http.Request) {
	out, err := json.Marshal(wl)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
	} else {
		w.Write(out)
	}
}

type handler struct {
	h func(http.ResponseWriter, *http.Request)
}

func newHandler(h func(w http.ResponseWriter, r *http.Request)) http.Handler {
	return &handler{h: h}
}

func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	h.h(w, r)
}

func main() {
	root := flag.String("root", "files/", "file server root")
	flag.Parse()

	fileServer := http.StripPrefix("/files/",
		http.FileServer(http.Dir(*root)))
	wl.Add(net.IP{127, 0, 0, 1})

	adminWL := whitelist.NewBasic()
	adminWL.Add(net.IP{127, 0, 0, 1})
	adminWL.Add(net.ParseIP("::1"))

	protFiles, err := whitelist.NewHandler(fileServer, nil, wl)
	if err != nil {
		log.Fatalf("%v", err)
	}

	addHandler, err := whitelist.NewHandlerFunc(addIP, nil, adminWL)
	if err != nil {
		log.Fatalf("%v", err)
	}

	delHandler, err := whitelist.NewHandlerFunc(delIP, nil, adminWL)
	if err != nil {
		log.Fatalf("%v", err)
	}

	dumpHandler, err := whitelist.NewHandlerFunc(dumpWhitelist, nil, adminWL)
	if err != nil {
		log.Fatalf("%v", err)
	}

	http.Handle("/files/", protFiles)
	http.Handle("/add", addHandler)
	http.Handle("/del", delHandler)
	http.Handle("/dump", dumpHandler)

	log.Println("Serving files on :8080")
	log.Fatal(http.ListenAndServe(":8080", nil))
}