Merge pull request #574 from lucas-clemente/fix-569

drop version negotiation packets that list the version the client chose

client.go

@@ -183,9 +183,11 @@ func (c *client) handlePacket(remoteAddr net.Addr, packet []byte) error {
 
 func (c *client) handlePacketWithVersionFlag(hdr *PublicHeader) error {
 	for _, v := range hdr.SupportedVersions {
-		// check if the server sent the offered version in supported versions
 		if v == c.version {
-			return qerr.Error(qerr.InvalidVersionNegotiationPacket, "Server already supports client's version and should have accepted the connection.")
+			// the version negotiation packet contains the version that we offered
+			// this might be a packet sent by an attacker (or by a terribly broken server implementation)
+			// ignore it
+			return nil
 		}
 	}
 

client_test.go

@@ -265,9 +265,11 @@ var _ = Describe("Client", func() {
 			Consistently(func() bool { return versionNegotiateConnStateCalled }).Should(BeFalse())
 		})
 
-		It("errors if the server should have accepted the offered version", func() {
-			err := cl.handlePacket(nil, getVersionNegotiation([]protocol.VersionNumber{cl.version}))
-			Expect(err).To(MatchError(qerr.Error(qerr.InvalidVersionNegotiationPacket, "Server already supports client's version and should have accepted the connection.")))
+		It("drops version negotiation packets that contain the offered version", func() {
+			ver := cl.version
+			err := cl.handlePacket(nil, getVersionNegotiation([]protocol.VersionNumber{ver}))
+			Expect(err).ToNot(HaveOccurred())
+			Expect(cl.version).To(Equal(ver))
 		})
 	})
 })