Implement support for whitelists, default-deny/allow (#8)

Implement support for whitelists, default-deny/allow

README.md

@@ -33,12 +33,20 @@ f := NewFilters()
 
 // filter out addresses on the 192.168 subnet
 _, ipnet, _ := net.ParseCIDR("192.168.0.0/16")
-f.AddDialFilter(ipnet)
-
+f.AddFilter(ipnet, ActionDeny)
 
 // check if an address is blocked
 lanaddr, _ := ma.NewMultiaddr("/ip4/192.168.0.17/tcp/4050")
 fmt.Println(f.AddrBlocked(lanaddr))
+
+// the default for a filter is accept, but we can change that
+f.RemoveLiteral(ipnet)
+f.DefaultAction = ActionDeny
+fmt.Println(f.AddrBlocked(lanaddr))
+
+// we can now allow the local LAN, denying everything else
+f.AddFilter(ipnet, ActionAccept)
+fmt.Println(f.AddrBlocked(lanaddr))
 ```
 
 ## Contribute

filter.go

@@ -8,60 +8,157 @@ import (
 	manet "github.com/multiformats/go-multiaddr-net"
 )
 
+// Action is an enum modelling all possible filter actions.
+type Action int32
+
+const (
+	ActionNone Action = iota // zero value.
+	ActionAccept
+	ActionDeny
+)
+
+type filterEntry struct {
+	f      net.IPNet
+	action Action
+}
+
+// Filters is a structure representing a collection of accept/deny
+// net.IPNet filters, together with the DefaultAction flag, which
+// represents the default filter policy.
+//
+// Note that the last policy added to the Filters is authoritative.
 type Filters struct {
+	DefaultAction Action
+
 	mu      sync.RWMutex
-	filters map[string]*net.IPNet
+	filters []*filterEntry
 }
 
+// NewFilters constructs and returns a new set of net.IPNet filters.
+// By default, the new filter accepts all addresses.
 func NewFilters() *Filters {
 	return &Filters{
-		filters: make(map[string]*net.IPNet),
+		DefaultAction: ActionAccept,
+		filters:       make([]*filterEntry, 0),
 	}
 }
 
+func (fs *Filters) find(ipnet net.IPNet) (int, *filterEntry) {
+	s := ipnet.String()
+	for idx, ft := range fs.filters {
+		if ft.f.String() == s {
+			return idx, ft
+		}
+	}
+	return -1, nil
+}
+
+// AddDialFilter adds a deny rule to this Filters set. Hosts
+// matching the given net.IPNet filter will be denied, unless
+// another rule is added which states that they should be accepted.
+//
+// No effort is made to prevent duplication of filters, or to simplify
+// the filters list.
+//
+// DEPRECATED. Use AddFilter.
 func (fs *Filters) AddDialFilter(f *net.IPNet) {
+	fs.AddFilter(*f, ActionDeny)
+}
+
+// AddFilter adds a rule to the Filters set, enforcing the desired action for
+// the provided IPNet mask.
+func (fs *Filters) AddFilter(ipnet net.IPNet, action Action) {
+	fs.mu.Lock()
+	defer fs.mu.Unlock()
+
+	if _, f := fs.find(ipnet); f != nil {
+		f.action = action
+	} else {
+		fs.filters = append(fs.filters, &filterEntry{ipnet, action})
+	}
+}
+
+// RemoveLiteral removes the first filter associated with the supplied IPNet,
+// returning whether something was removed or not. It makes no distinction
+// between whether the rule is an accept or a deny.
+func (fs *Filters) RemoveLiteral(ipnet net.IPNet) (removed bool) {
 	fs.mu.Lock()
 	defer fs.mu.Unlock()
-	fs.filters[f.String()] = f
+
+	if idx, _ := fs.find(ipnet); idx != -1 {
+		fs.filters = append(fs.filters[:idx], fs.filters[idx+1:]...)
+		return true
+	}
+	return false
 }
 
-func (f *Filters) AddrBlocked(a ma.Multiaddr) bool {
+// AddrBlocked parses a ma.Multiaddr and, if a valid netip is found, it applies the
+// Filter set rules, returning true if the given address should be denied, and false if
+// the given address is accepted.
+//
+// If a parsing error occurs, or no filter matches, the Filters'
+// default is returned.
+//
+// TODO: currently, the last filter to match wins always, but it shouldn't be that way.
+//  Instead, the highest-specific last filter should win; that way more specific filters
+//  override more general ones.
+func (fs *Filters) AddrBlocked(a ma.Multiaddr) (deny bool) {
 	maddr := ma.Split(a)
 	if len(maddr) == 0 {
-		return false
+		return fs.DefaultAction == ActionDeny
 	}
 	netaddr, err := manet.ToNetAddr(maddr[0])
 	if err != nil {
-		// if we can't parse it, it's probably not blocked
-		return false
+		// if we can't parse it, it's probably not blocked.
+		return fs.DefaultAction == ActionDeny
 	}
 	netip := net.ParseIP(netaddr.String())
 	if netip == nil {
-		return false
+		return fs.DefaultAction == ActionDeny
 	}
 
-	f.mu.RLock()
-	defer f.mu.RUnlock()
-	for _, ft := range f.filters {
-		if ft.Contains(netip) {
-			return true
+	fs.mu.RLock()
+	defer fs.mu.RUnlock()
+
+	action := fs.DefaultAction
+	for _, ft := range fs.filters {
+		if ft.f.Contains(netip) {
+			action = ft.action
 		}
 	}
-	return false
+
+	return action == ActionDeny
+}
+
+// Filters returns the list of DENY net.IPNet masks. For backwards compatibility.
+//
+// A copy of the filters is made prior to returning, so the inner state is not exposed.
+//
+// DEPRECATED. Use FiltersForAction().
+func (fs *Filters) Filters() (result []*net.IPNet) {
+	ffa := fs.FiltersForAction(ActionDeny)
+	for _, res := range ffa {
+		result = append(result, &res)
+	}
+	return result
 }
 
-func (f *Filters) Filters() []*net.IPNet {
-	var out []*net.IPNet
-	f.mu.RLock()
-	defer f.mu.RUnlock()
-	for _, ff := range f.filters {
-		out = append(out, ff)
+func (fs *Filters) ActionForFilter(ipnet net.IPNet) (action Action, ok bool) {
+	if _, f := fs.find(ipnet); f != nil {
+		return f.action, true
 	}
-	return out
+	return ActionNone, false
 }
 
-func (f *Filters) Remove(ff *net.IPNet) {
-	f.mu.Lock()
-	defer f.mu.Unlock()
-	delete(f.filters, ff.String())
+// FiltersForAction returns the filters associated with the indicated action.
+func (fs *Filters) FiltersForAction(action Action) (result []net.IPNet) {
+	fs.mu.RLock()
+	defer fs.mu.RUnlock()
+
+	for _, ff := range fs.filters {
+		if ff.action == action {
+			result = append(result, ff.f)
+		}
+	}
+	return result
 }

filter_test.go

@@ -7,7 +7,7 @@ import (
 	ma "github.com/multiformats/go-multiaddr"
 )
 
-func TestFilter(t *testing.T) {
+func TestFilterBlocking(t *testing.T) {
 	f := NewFilters()
 
 	_, ipnet, _ := net.ParseCIDR("0.1.2.3/24")
@@ -16,7 +16,14 @@ func TestFilter(t *testing.T) {
 	if len(filters) != 1 {
 		t.Fatal("Expected only 1 filter")
 	}
-	f.Remove(filters[0])
+
+	if a, ok := f.ActionForFilter(*ipnet); !ok || a != ActionDeny {
+		t.Fatal("Expected filter with DENY action")
+	}
+
+	if !f.RemoveLiteral(*filters[0]) {
+		t.Error("expected true value from RemoveLiteral")
+	}
 
 	for _, cidr := range []string{
 		"1.2.3.0/24",
@@ -28,6 +35,7 @@ func TestFilter(t *testing.T) {
 		f.AddDialFilter(ipnet)
 	}
 
+	// These addresses should all be blocked
 	for _, blocked := range []string{
 		"/ip4/1.2.3.4/tcp/123",
 		"/ip4/4.3.2.1/udp/123",
@@ -43,19 +51,129 @@ func TestFilter(t *testing.T) {
 		}
 	}
 
-	for _, notBlocked := range []string{
+	// test that other net intervals are not blocked
+	for _, addr := range []string{
 		"/ip4/1.2.4.1/tcp/123",
 		"/ip4/4.3.2.2/udp/123",
 		"/ip6/fe00::1/tcp/321",
 		"/ip6/fc00::2/udp/321",
 		"",
 	} {
-		maddr, err := ma.NewMultiaddr(notBlocked)
+		maddr, err := ma.NewMultiaddr(addr)
+		if err != nil {
+			t.Error(err)
+		}
+		if f.AddrBlocked(maddr) {
+			t.Fatalf("expected %s to not be blocked", addr)
+		}
+	}
+}
+
+func TestFilterWhitelisting(t *testing.T) {
+	f := NewFilters()
+
+	// Add default reject filter
+	f.DefaultAction = ActionDeny
+
+	// Add a whitelist
+	_, ipnet, _ := net.ParseCIDR("1.2.3.0/24")
+	f.AddFilter(*ipnet, ActionAccept)
+
+	if a, ok := f.ActionForFilter(*ipnet); !ok || a != ActionAccept {
+		t.Fatal("Expected filter with ACCEPT action")
+	}
+
+	// That /24 should now be allowed
+	for _, addr := range []string{
+		"/ip4/1.2.3.1/tcp/123",
+		"/ip4/1.2.3.254/tcp/123",
+		"/ip4/1.2.3.254/udp/321",
+	} {
+		maddr, err := ma.NewMultiaddr(addr)
 		if err != nil {
 			t.Error(err)
 		}
 		if f.AddrBlocked(maddr) {
-			t.Fatalf("expected %s to not be blocked", notBlocked)
+			t.Fatalf("expected %s to be whitelisted", addr)
+		}
+	}
+
+	// No policy matches these maddrs, they should be blocked by default
+	for _, blocked := range []string{
+		"/ip4/1.2.4.4/tcp/123",
+		"/ip4/4.3.2.1/udp/123",
+		"/ip6/fd00::2/tcp/321",
+		"/ip6/fc00::1/udp/321",
+	} {
+		maddr, err := ma.NewMultiaddr(blocked)
+		if err != nil {
+			t.Error(err)
+		}
+		if !f.AddrBlocked(maddr) {
+			t.Fatalf("expected %s to be blocked", blocked)
+		}
+	}
+}
+
+func TestFiltersRemoveRules(t *testing.T) {
+	f := NewFilters()
+
+	ips := []string{
+		"/ip4/1.2.3.1/tcp/123",
+		"/ip4/1.2.3.254/tcp/123",
+	}
+
+	// Add default reject filter
+	f.DefaultAction = ActionDeny
+
+	// Add whitelisting
+	_, ipnet, _ := net.ParseCIDR("1.2.3.0/24")
+	f.AddFilter(*ipnet, ActionAccept)
+
+	if a, ok := f.ActionForFilter(*ipnet); !ok || a != ActionAccept {
+		t.Fatal("Expected filter with ACCEPT action")
+	}
+
+	// these are all whitelisted, should be OK
+	for _, addr := range ips {
+		maddr, err := ma.NewMultiaddr(addr)
+		if err != nil {
+			t.Error(err)
+		}
+		if f.AddrBlocked(maddr) {
+			t.Fatalf("expected %s to be whitelisted", addr)
+		}
+	}
+
+	// Test removing the filter. It'll remove multiple, so make a dupe &
+	// a complement
+	f.AddDialFilter(ipnet)
+
+	// Show that they all apply, these are now blacklisted & should fail
+	for _, addr := range ips {
+		maddr, err := ma.NewMultiaddr(addr)
+		if err != nil {
+			t.Error(err)
+		}
+		if !f.AddrBlocked(maddr) {
+			t.Fatalf("expected %s to be blacklisted", addr)
+		}
+	}
+
+	// remove those rules
+	if !f.RemoveLiteral(*ipnet) {
+		t.Error("expected true value from RemoveLiteral")
+	}
+
+	// our default is reject, so the 1.2.3.0/24 should be rejected now,
+	// along with everything else
+	for _, addr := range ips {
+		maddr, err := ma.NewMultiaddr(addr)
+		if err != nil {
+			t.Error(err)
+		}
+		if !f.AddrBlocked(maddr) {
+			t.Fatalf("expected %s to be blocked", addr)
 		}
 	}
 }