BUG/MEDIUM: ssl: fix an out-of-bounds read on SSL_CTX switch with a .sctl file

BUG/MEDIUM: ssl: fix an out-of-bounds read on SSL_CTX switch with a .sctl file

A certificate's .sctl sidecar registers extension 18 only on that
certificate's SSL_CTX. Connections start on initial_ctx without this
extension, then switch contexts in the ClientHello callback.

OpenSSL sizes the received-extensions array from the initial context but
parses it using the selected context's extension count. An unauthenticated
ClientHello selecting a certificate with a .sctl file can therefore trigger
an out-of-bounds read in tls_parse_all_extensions(). Depending on the heap
contents, the parser may also write past the array and read adjacent data.

Register the extension in the same order on every switchable frontend
context. The add callback omits it when the selected context has no SCT
list. Skip QUIC contexts because native OpenSSL's SSL_set_SSL_CTX() reads
freed memory when merging the transport parameters extension with custom
extensions. Skip registration on AWS-LC, which owns extension 18.

Workaround: remove "sctl" from "ssl-load-extra-files" or remove the .sctl files.

This should be backported to all supported versions.

Reported-by: Finlay Moss <fmoss2003@gmail.com>