middleware: sanitize max scrape infohashes

Fixes #268.

contrib/helm/chihaya/values.yaml

@@ -16,6 +16,7 @@ config:
     prometheus_addr: 0.0.0.0:6880
     max_numwant: 50
     default_numwant: 25
+    max_scrape_infohashes: 50
     http:
       addr: 0.0.0.0:6881
       allow_ip_spoofing: true

example_config.yaml

@@ -14,6 +14,9 @@ chihaya:
   # The default number of peers returned in an announce.
   default_numwant: 25
 
+  # The number of infohashes a single scrape can request before being truncated.
+  max_scrape_infohashes: 50
+
   # This block defines configuration for the tracker's HTTP interface.
   # If you do not wish to run this, delete this section.
   http:

middleware/hooks.go

@@ -83,8 +83,9 @@ var ErrInvalidIP = errors.New("invalid IP")
 //     IPv6. Sets the Peer.AddressFamily field accordingly. Truncates IPv4
 //     addresses to have a length of 4 bytes.
 type sanitizationHook struct {
-	maxNumWant     uint32
-	defaultNumWant uint32
+	maxNumWant          uint32
+	defaultNumWant      uint32
+	maxScrapeInfoHashes uint32
 }
 
 func (h *sanitizationHook) HandleAnnounce(ctx context.Context, req *bittorrent.AnnounceRequest, resp *bittorrent.AnnounceResponse) (context.Context, error) {
@@ -109,6 +110,10 @@ func (h *sanitizationHook) HandleAnnounce(ctx context.Context, req *bittorrent.A
 }
 
 func (h *sanitizationHook) HandleScrape(ctx context.Context, req *bittorrent.ScrapeRequest, resp *bittorrent.ScrapeResponse) (context.Context, error) {
+	if len(req.InfoHashes) > int(h.maxScrapeInfoHashes) {
+		req.InfoHashes = req.InfoHashes[:h.maxScrapeInfoHashes]
+	}
+
 	return ctx, nil
 }
 

middleware/middleware.go

@@ -15,9 +15,10 @@ import (
 
 // Config holds the configuration common across all middleware.
 type Config struct {
-	AnnounceInterval time.Duration `yaml:"announce_interval"`
-	MaxNumWant       uint32        `yaml:"max_numwant"`
-	DefaultNumWant   uint32        `yaml:"default_numwant"`
+	AnnounceInterval    time.Duration `yaml:"announce_interval"`
+	MaxNumWant          uint32        `yaml:"max_numwant"`
+	DefaultNumWant      uint32        `yaml:"default_numwant"`
+	MaxScrapeInfoHashes uint32        `yaml:"max_scrape_infohashes"`
 }
 
 var _ frontend.TrackerLogic = &Logic{}
@@ -28,7 +29,7 @@ func NewLogic(cfg Config, peerStore storage.PeerStore, preHooks, postHooks []Hoo
 	l := &Logic{
 		announceInterval: cfg.AnnounceInterval,
 		peerStore:        peerStore,
-		preHooks:         []Hook{&sanitizationHook{maxNumWant: cfg.MaxNumWant, defaultNumWant: cfg.DefaultNumWant}},
+		preHooks:         []Hook{&sanitizationHook{cfg.MaxNumWant, cfg.DefaultNumWant, cfg.MaxScrapeInfoHashes}},
 		postHooks:        append(postHooks, &swarmInteractionHook{store: peerStore}),
 	}