The following review has been posted through the commitfest application:
make installcheck-world: not tested
Implements feature: not tested
Spec compliant: not tested
Documentation: not tested
This is an interesting feature on PostgreSQL server side where it can swap the
certificate settings based on the incoming hostnames in SNI field in client
hello message.
I think this patch resonate with a patch I shared awhile ago
( https://commitfest.postgresql.org/48/4924/ ) that adds multiple certificate
support on the libpq client side while this patch adds multiple certificate
support on the server side. My patch allows user to supply multiple certs, keys,
sslpasswords in comma separated format and the libpq client will pick one that
matches the CA issuer names sent by the server. In relation with your patch,
this CA issuer name would match the CA certificate configured in pg_hosts.cfg.
I had a look at the patch and here's my comments:
+ <para>
+ <productname>PostgreSQL</productname> can be configured for
+ <acronym>SNI</acronym> using the <filename>pg_hosts.conf</filename>
+ configuration file. <productname>PostgreSQL</productname> inspects the TLS
+ hostname extension in the SSL connection handshake, and selects the right
+ SSL certificate, key and CA certificate to use for the connection.
+ </para>
pg_hosts should also have sslpassword_command just like in the postgresql.conf in
case the sslkey for a particular host is encrypted with a different password.
+ /*
+ * Install SNI TLS extension callback in case the server is configured to
+ * validate hostnames.
+ */
+ if (ssl_snimode != SSL_SNIMODE_OFF)
+ SSL_CTX_set_tlsext_servername_callback(context, sni_servername_cb);
If libpq client does not provide SNI, this callback will not be called, so there
is not a chance to check for a hostname match from pg_hosts, swap the TLS CONTEXT,
or possibly reject the connection even in strict mode. The TLS handshake in such
case shall proceed and server will use the certificate specified in
postgresql.conf (if these are loaded) to complete the handshake with the client.
There is a comment in the patch that reads:
> - strict: only pg_hosts.conf is loaded and the TLS extension hostname
> MUST be passed and MUST have a match in the configuration, else the
> connection is refused.
I am not sure if it implies that if ssl_snimode is strict, then the normal ssl_cert,
ssl_key and ca_cert…etc settings in postgresql.conf are ignored?
thank you
Cary Huang
-------------
HighGo Software Inc. (Canada)
cary.huang@highgo.ca
www.highgo.ca