downloader: move internal subnet validation into http Transport

router/downloader/downloader.go

@@ -20,20 +20,58 @@ import (
 	"github.com/pterodactyl/wings/server"
 )
 
-var client = &http.Client{
-	Timeout: time.Hour * 12,
-	// Disallow any redirect on an HTTP call. This is a security requirement: do not modify
-	// this logic without first ensuring that the new target location IS NOT within the current
-	// instance's local network.
-	//
-	// This specific error response just causes the client to not follow the redirect and
-	// returns the actual redirect response to the caller. Not perfect, but simple and most
-	// people won't be using URLs that redirect anyways hopefully?
-	//
-	// We'll re-evaluate this down the road if needed.
-	CheckRedirect: func(req *http.Request, via []*http.Request) error {
-		return http.ErrUseLastResponse
-	},
+var client *http.Client
+
+func init() {
+	dialer := &net.Dialer{
+		LocalAddr: nil,
+	}
+
+	trnspt := http.DefaultTransport.(*http.Transport).Clone()
+	trnspt.DialContext = func(ctx context.Context, network, addr string) (net.Conn, error) {
+		c, err := dialer.DialContext(ctx, network, addr)
+		if err != nil {
+			return nil, errors.WithStack(err)
+		}
+
+		ipStr, _, err := net.SplitHostPort(c.RemoteAddr().String())
+		if err != nil {
+			return c, errors.WithStack(err)
+		}
+		ip := net.ParseIP(ipStr)
+		if ip == nil {
+			return c, errors.WithStack(ErrInvalidIPAddress)
+		}
+		if ip.IsLoopback() || ip.IsLinkLocalUnicast() || ip.IsLinkLocalMulticast() || ip.IsInterfaceLocalMulticast() {
+			return c, errors.WithStack(ErrInternalResolution)
+		}
+		for _, block := range internalRanges {
+			if !block.Contains(ip) {
+				continue
+			}
+			return c, errors.WithStack(ErrInternalResolution)
+		}
+		return c, nil
+	}
+
+	client = &http.Client{
+		Timeout: time.Hour * 12,
+
+		Transport: trnspt,
+
+		// Disallow any redirect on an HTTP call. This is a security requirement: do not modify
+		// this logic without first ensuring that the new target location IS NOT within the current
+		// instance's local network.
+		//
+		// This specific error response just causes the client to not follow the redirect and
+		// returns the actual redirect response to the caller. Not perfect, but simple and most
+		// people won't be using URLs that redirect anyways hopefully?
+		//
+		// We'll re-evaluate this down the road if needed.
+		CheckRedirect: func(req *http.Request, via []*http.Request) error {
+			return http.ErrUseLastResponse
+		},
+	}
 }
 
 var instance = &Downloader{
@@ -143,12 +181,6 @@ func (dl *Download) Execute() error {
 	dl.cancelFunc = &cancel
 	defer dl.Cancel()
 
-	// Always ensure that we're checking the destination for the download to avoid a malicious
-	// user from accessing internal network resources.
-	if err := dl.isExternalNetwork(ctx); err != nil {
-		return err
-	}
-
 	// At this point we have verified the destination is not within the local network, so we can
 	// now make a request to that URL and pull down the file, saving it to the server's data
 	// directory.
@@ -243,59 +275,6 @@ func (dl *Download) counter(contentLength int64) *Counter {
 	}
 }
 
-// Verifies that a given download resolves to a location not within the current local
-// network for the machine. If the final destination of a resource is within the local
-// network an ErrInternalResolution error is returned.
-func (dl *Download) isExternalNetwork(ctx context.Context) error {
-	dialer := &net.Dialer{
-		LocalAddr: nil,
-	}
-
-	host := dl.req.URL.Host
-
-	// This cluster-fuck of math and integer shit converts an integer IP into a proper IPv4.
-	// For example: 16843009 would become 1.1.1.1
-	//if i, err := strconv.ParseInt(host, 10, 64); err == nil {
-	//	host = strconv.FormatInt((i>>24)&0xFF, 10) + "." + strconv.FormatInt((i>>16)&0xFF, 10) + "." + strconv.FormatInt((i>>8)&0xFF, 10) + "." + strconv.FormatInt(i&0xFF, 10)
-	//}
-
-	if _, _, err := net.SplitHostPort(host); err != nil {
-		if !strings.Contains(err.Error(), "missing port in address") {
-			return errors.WithStack(err)
-		}
-		switch dl.req.URL.Scheme {
-		case "http":
-			host += ":80"
-		case "https":
-			host += ":443"
-		}
-	}
-
-	c, err := dialer.DialContext(ctx, "tcp", host)
-	if err != nil {
-		return errors.WithStack(err)
-	}
-	_ = c.Close()
-
-	ipStr, _, err := net.SplitHostPort(c.RemoteAddr().String())
-	if err != nil {
-		return errors.WithStack(err)
-	}
-	ip := net.ParseIP(ipStr)
-	if ip == nil {
-		return errors.WithStack(ErrInvalidIPAddress)
-	}
-	if ip.IsLoopback() || ip.IsLinkLocalUnicast() || ip.IsLinkLocalMulticast() || ip.IsInterfaceLocalMulticast() {
-		return errors.WithStack(ErrInternalResolution)
-	}
-	for _, block := range internalRanges {
-		if block.Contains(ip) {
-			return errors.WithStack(ErrInternalResolution)
-		}
-	}
-	return nil
-}
-
 // Downloader represents a global downloader that keeps track of all currently processing downloads
 // for the machine.
 type Downloader struct {