From 9a44cf9ff8a933cdcc556cb7b3a9f4d66b990de7 Mon Sep 17 00:00:00 2001
From: Juliusz Chroboczek <jch@irif.fr>
Date: Tue, 2 Feb 2021 22:32:16 +0100
Subject: [PATCH] Avoid infinite loop in CreateOffer

If the local description keeps getting changed, or in case of a but
in Pion, CreateOffer never terminates, which could cause client software
to hang.  Set an arbitrary bound on the number of iterations.
---
 peerconnection.go | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/peerconnection.go b/peerconnection.go
index f8c0d153e91..ca845fc576b 100644
--- a/peerconnection.go
+++ b/peerconnection.go
@@ -6,6 +6,7 @@ import (
 	"crypto/ecdsa"
 	"crypto/elliptic"
 	"crypto/rand"
+	"errors"
 	"fmt"
 	"io"
 	"strconv"
@@ -576,6 +577,8 @@ func (pc *PeerConnection) hasLocalDescriptionChanged(desc *SessionDescription) b
 	return false
 }
 
+var errExcessiveRetries = errors.New("excessive retries in CreateOffer")
+
 // CreateOffer starts the PeerConnection and generates the localDescription
 // https://w3c.github.io/webrtc-pc/#dom-rtcpeerconnection-createoffer
 func (pc *PeerConnection) CreateOffer(options *OfferOptions) (SessionDescription, error) { //nolint:gocognit
@@ -603,6 +606,7 @@ func (pc *PeerConnection) CreateOffer(options *OfferOptions) (SessionDescription
 	// audio RTCRtpTransceiver was added to connection, but while performing the in-parallel
 	// steps to create an offer, a video RTCRtpTransceiver was added, requiring additional
 	// inspection of video system resources.
+	count := 0
 	for {
 		// We cache current transceivers to ensure they aren't
 		// mutated during offer generation. We later check if they have
@@ -673,6 +677,10 @@ func (pc *PeerConnection) CreateOffer(options *OfferOptions) (SessionDescription
 		if isPlanB || !pc.hasLocalDescriptionChanged(&offer) {
 			break
 		}
+		count++
+		if count >= 128 {
+			return SessionDescription{}, errExcessiveRetries
+		}
 	}
 
 	pc.lastOffer = offer.SDP