ERL-803: Server-initiated renegotiation after client data fails with 'bad_record_mac'

[OTP-Maintainer]

Original reporter: voltone
Affected versions: OTP-21.1, OTP-21.2
Fixed in version: OTP-21.2.1
Component: ssl
Migrated from: https://bugs.erlang.org/browse/ERL-803

---

Originally reported by Nico Caille on ElixirForum:
https://elixirforum.com/t/hackney-and-client-certificates-error-closed/18723

Since OTP 21.1, if an Erlang client has previously sent data to a server and subsequently responds to a HelloRequest from the server with a renegotiation ClientHello, that message is malformed, causing the connection to fail. Note that this scenario is not covered by the ssl test suite (it tests renegotiation without prior data exchange).

It was originally reported with Hackney in combination with a Microsoft IIS server, which parses the client's HTTP request before deciding it wants to ask for a client certificate. IIS does not send an alert, but closes the TCP connection.

The issue can be reduced to a minimal case with 'ssl:connect' to 'openssl s_server', sending some data from the client and then triggering renegotiation on the server. This results in a bad_record_mac fatal alert.

In OTP 21.0.9 and earlier releases, the same scenario succeeds, so I suspect the issue was introduced in https://github.com/erlang/otp/commit/d87ac1c55188f5ba5cdf72384125d94d42118c18

I created a crude test case that reproduces the issue. A diff for the test suite (against master) and the test output attached.

[OTP-Maintainer]

ingela said:

Thank you for the test case, I have confirmed that it fails.  I agree with you that the sender process
commit is a suspect. It is needed to avoid a deadlock but alas it makes renegotiation harder to get correct. We will investigate.

[OTP-Maintainer]

ingela said:

The following branch  ingela/ssl/renegotiate-with-new-tls-sender
 in my git repo:  https://github.com/IngelaAndin/otp.git fixes the problem for me.

[OTP-Maintainer]

voltone said:

Confirmed against the original IIS server, with both httpc and Hackney

[OTP-Maintainer]

ingela said:

Thank you, I have included the patch in our nightly build and  we will make a patch soonish.
Can not promise before new year but with a little luck... 

[OTP-Maintainer]

voltone said:

Thanks!