From 47b5e67345f6e271ce214e66d1843f411ed28127 Mon Sep 17 00:00:00 2001
From: Jimmy Zelinskie <jimmy.zelinskie+git@gmail.com>
Date: Sun, 8 Oct 2017 17:35:50 -0400
Subject: [PATCH] frontend/udp: add request sanitization

---
 frontend/udp/frontend.go | 11 +++++---
 frontend/udp/parser.go   | 58 +++++++++++++++++++++++++++-------------
 2 files changed, 46 insertions(+), 23 deletions(-)

diff --git a/frontend/udp/frontend.go b/frontend/udp/frontend.go
index 4ecbf85..e50d182 100644
--- a/frontend/udp/frontend.go
+++ b/frontend/udp/frontend.go
@@ -70,8 +70,8 @@ type Config struct {
 	Addr                string        `yaml:"addr"`
 	PrivateKey          string        `yaml:"private_key"`
 	MaxClockSkew        time.Duration `yaml:"max_clock_skew"`
-	AllowIPSpoofing     bool          `yaml:"allow_ip_spoofing"`
 	EnableRequestTiming bool          `yaml:"enable_request_timing"`
+	ParseOptions        `yaml:",inline"`
 }
 
 // LogFields renders the current config as a set of Logrus fields.
@@ -80,8 +80,11 @@ func (cfg Config) LogFields() log.Fields {
 		"addr":                cfg.Addr,
 		"privateKey":          cfg.PrivateKey,
 		"maxClockSkew":        cfg.MaxClockSkew,
-		"allowIPSpoofing":     cfg.AllowIPSpoofing,
 		"enableRequestTiming": cfg.EnableRequestTiming,
+		"allowIPSpoofing":     cfg.AllowIPSpoofing,
+		"maxNumWant":          cfg.MaxNumWant,
+		"defaultNumWant":      cfg.DefaultNumWant,
+		"maxScrapeInfohashes": cfg.MaxScrapeInfoHashes,
 	}
 }
 
@@ -278,7 +281,7 @@ func (t *Frontend) handleRequest(r Request, w ResponseWriter) (actionName string
 		actionName = "announce"
 
 		var req *bittorrent.AnnounceRequest
-		req, err = ParseAnnounce(r, t.AllowIPSpoofing, actionID == announceV6ActionID)
+		req, err = ParseAnnounce(r, actionID == announceV6ActionID, t.ParseOptions)
 		if err != nil {
 			WriteError(w, txID, err)
 			return
@@ -302,7 +305,7 @@ func (t *Frontend) handleRequest(r Request, w ResponseWriter) (actionName string
 		actionName = "scrape"
 
 		var req *bittorrent.ScrapeRequest
-		req, err = ParseScrape(r)
+		req, err = ParseScrape(r, t.ParseOptions)
 		if err != nil {
 			WriteError(w, txID, err)
 			return
diff --git a/frontend/udp/parser.go b/frontend/udp/parser.go
index 9bc453c..e35e3b4 100644
--- a/frontend/udp/parser.go
+++ b/frontend/udp/parser.go
@@ -45,14 +45,19 @@ var (
 	errUnknownOptionType = bittorrent.ClientError("unknown option type")
 )
 
+// ParseOptions is the configuration used to parse an Announce Request.
+//
+// If AllowIPSpoofing is true, IPs provided via params will be used.
+type ParseOptions struct {
+	AllowIPSpoofing             bool `yaml:"allowIPSpoofing"`
+	bittorrent.RequestSanitizer `yaml:",inline"`
+}
+
 // ParseAnnounce parses an AnnounceRequest from a UDP request.
 //
-// If allowIPSpoofing is true, IPs provided via params will be used.
-//
-// If v6 is true the announce will be parsed as an IPv6 announce "the
-// opentracker way", see
+// If v6 is true, the announce is parsed the "opentracker way":
 // http://opentracker.blog.h3q.com/2007/12/28/the-ipv6-situation/
-func ParseAnnounce(r Request, allowIPSpoofing, v6 bool) (*bittorrent.AnnounceRequest, error) {
+func ParseAnnounce(r Request, v6 bool, opts ParseOptions) (*bittorrent.AnnounceRequest, error) {
 	ipEnd := 84 + net.IPv4len
 	if v6 {
 		ipEnd = 84 + net.IPv6len
@@ -74,12 +79,14 @@ func ParseAnnounce(r Request, allowIPSpoofing, v6 bool) (*bittorrent.AnnounceReq
 	}
 
 	ip := r.IP
+	ipProvided := false
 	ipbytes := r.Packet[84:ipEnd]
-	if allowIPSpoofing {
+	if opts.AllowIPSpoofing {
 		// Make sure the bytes are copied to a new slice.
 		copy(ip, net.IP(ipbytes))
+		ipProvided = true
 	}
-	if !allowIPSpoofing && r.IP == nil {
+	if !opts.AllowIPSpoofing && r.IP == nil {
 		// We have no IP address to fallback on.
 		return nil, errMalformedIP
 	}
@@ -92,20 +99,29 @@ func ParseAnnounce(r Request, allowIPSpoofing, v6 bool) (*bittorrent.AnnounceReq
 		return nil, err
 	}
 
-	return &bittorrent.AnnounceRequest{
-		Event:      eventIDs[eventID],
-		InfoHash:   bittorrent.InfoHashFromBytes(infohash),
-		NumWant:    uint32(numWant),
-		Left:       left,
-		Downloaded: downloaded,
-		Uploaded:   uploaded,
+	request := &bittorrent.AnnounceRequest{
+		Event:           eventIDs[eventID],
+		InfoHash:        bittorrent.InfoHashFromBytes(infohash),
+		NumWant:         uint32(numWant),
+		Left:            left,
+		Downloaded:      downloaded,
+		Uploaded:        uploaded,
+		IPProvided:      ipProvided,
+		NumWantProvided: true,
+		EventProvided:   true,
 		Peer: bittorrent.Peer{
 			ID:   bittorrent.PeerIDFromBytes(peerID),
 			IP:   bittorrent.IP{IP: ip},
 			Port: port,
 		},
 		Params: params,
-	}, nil
+	}
+
+	if err := opts.SanitizeAnnounce(request); err != nil {
+		return nil, err
+	}
+
+	return request, nil
 }
 
 type buffer struct {
@@ -170,7 +186,7 @@ func handleOptionalParameters(packet []byte) (bittorrent.Params, error) {
 }
 
 // ParseScrape parses a ScrapeRequest from a UDP request.
-func ParseScrape(r Request) (*bittorrent.ScrapeRequest, error) {
+func ParseScrape(r Request, opts ParseOptions) (*bittorrent.ScrapeRequest, error) {
 	// If a scrape isn't at least 36 bytes long, it's malformed.
 	if len(r.Packet) < 36 {
 		return nil, errMalformedPacket
@@ -190,7 +206,11 @@ func ParseScrape(r Request) (*bittorrent.ScrapeRequest, error) {
 		r.Packet = r.Packet[20:]
 	}
 
-	return &bittorrent.ScrapeRequest{
-		InfoHashes: infohashes,
-	}, nil
+	// Sanitize the request.
+	request := &bittorrent.ScrapeRequest{InfoHashes: infohashes}
+	if err := opts.SanitizeScrape(request); err != nil {
+		return nil, err
+	}
+
+	return request, nil
 }