WebRTC: usrsctp is called with pointer as network address

When usrsctp is used with a custom transport, an address must be provided to usrsctp_conninput be used as the source and destination address of the incoming packet. WebRTC uses the address of the SctpTransport instance for this value. Unfortunately, this value is often transmitted to the peer, for example to validate signing of the cookie. This could allow an attacker access to the location in memory of the SctpTransport of a peer, bypassing ASLR.

To reproduce, place the following code on line 9529 of sctp_output.c. This will output the peer's address to the log:

        struct sctp_state_cookie cookie2;
        struct sctp_state_cookie* cookie3;
  cookie3 = sctp_get_next_param(cookie, 4, &cookie2, sizeof(struct sctp_state_cookie));

  LOGE(\"COOKIE INITACK ADDRESS %llx laddress %llx\", *((long long*)cookie3->address), *((long long*)cookie3->address));

Or, view the SCTP packets sent by WebRTC before they are sent to the encryption layer. They are full of pointers. 

This bug is subject to a 90 day disclosure deadline. After 90 days elapse,
the bug report will become visible to the public. The scheduled disclosure
date is 2020-Jul-28. Disclosure at an earlier date is possible if
agreed upon by all parties.

Related CVE Numbers: CVE-2020-6514.

# [2020-08-01]  #