Re: Security issues concerning pgsql replication

On Tue, Oct 27, 2020 at 12:34 PM xiebin (F) <xiebin18(at)huawei(dot)com> wrote:

> Perhaps you misunderstand me.
>
> It is not user-database, but master-slave interaction that I am
> concerning.
>
> The master-slave replication proceeds continually and requires no manual
> interference. Both master and slave’s private key are involved, but
> ssl_passphrase_command is only used to parse passphrase of master’s private
> key. Pgsql cannot get slave’s private key automatically, so replication
> failed. I’ve tried and proved it did not work.
>

Ah yeah, you're right. For the client, there is an API for a callback, but
yeah, not a connection string one.

So your method around that would be to use an openssl engine for storage of
it, such as a smartcard (that one you can set in the sslkey parameter).

> I refered to the list of pgsql’s authenticate methods but did not find an
> appropriate one for replication.
>
> https://www.postgresql.org/docs/12/client-authentication.html
>

Replication uses the *same* authentication methods as client connections.
There is no difference.

So you can use for example GSSAPI instead of clientcert, which would move
the responsibility over to your Kerberos system. Then you can set that one
up to require you to manually type in a password or equivalent to get t a
ticket, and configure expiry on that ticket.

//Magnus

*发件人:* Magnus Hagander [mailto:magnus(at)hagander(dot)net]
>
> *发送时间:* 2020年10月27日 17:00
> *收件人:* xiebin (F) <xiebin18(at)huawei(dot)com>
> *抄送:* pgsql-general(at)postgresql(dot)org; zhubo (C) <zhubo31(at)huawei(dot)com>;
> Zhuzheng (IT) <zhuzheng(at)huawei(dot)com>; houxiaowei <brian(dot)hou(at)huawei(dot)com>;
> yangshaobo (A) <yangshaobo6(at)huawei(dot)com>; mapinghu <mapinghu(at)huawei(dot)com>;
> Songyunpeng <songyunpeng(at)huawei(dot)com>; luoqi (F) <luoqi25(at)huawei(dot)com>
> *主题:* Re: Security issues concerning pgsql replication
>
>
>
>
>
>
>
> On Tue, Oct 27, 2020 at 9:52 AM xiebin (F) <xiebin18(at)huawei(dot)com> wrote:
>
> Hi,
>
>
>
> I was setting up a master/slave pgsql(version 12.4) cluster using stream
> replication. I found 3 ways to authenticate, but all of them has some
> security issue.
>
>
>
> 1. Disable authentication.
>
> *cat pg_hba.conf*
>
> * host all all 0/0 md5*
>
> * host replication xie 192.168.1.31/32
> <http://192.168.1.31/32> trust*
>
>
>
> In this case, untrusted users on slave may use pg_basebackup to stole data.
>
>
>
> 2. Using password.
>
> *cat pg_hba.conf*
>
> * host all all 0/0 md5*
>
> * host replication xie 192.168.1.31/32
> <http://192.168.1.31/32> md5*
>
>
>
> *cat /var/lib/pgsql/.pgpass (on slave)*
>
> * 192.168.1.30:5432:xie:mydb:xie*
>
>
>
> In this case, the password is stored unencrypted. File access control may
> help, but it’s not secure enough.
>
>
>
>
>
> Why not? The user who can read that file, can also read the entire
> database on the standby node already.
>
>
>
> 3. Using certificate.
>
> *cat pg_hba.conf*
>
> * host all all 0/0 md5*
>
> * hostssl replication xie 192.168.1.31/32
> <http://192.168.1.31/32> cert clientcert=1*
>
>
>
> *cat postgresql.conf | grep ssl*
>
> * ssl = on*
>
> *ssl_ca_file = 'root.crt'*
>
> *ssl_cert_file = 'server.crt'*
>
> *ssl_crl_file = ''*
>
> *ssl_key_file = 'server.key' *
>
>
>
> *cat recovery.conf*
>
> * primary_conninfo = 'host=192.168.1.30 port=5432 user=xie
> application_name=stream_relication sslrootcert=/tmp/root.crt
> sslcert=/tmp/xie.crt sslkey=/tmp/xie.key'*
>
> *restore_command = ''*
>
> *recovery_target_timeline = 'latest'*
>
> *primary_slot_name = 'rep_slot'*
>
>
>
> The certificates are created by official instructions
> https://www.postgresql.org/docs/12/ssl-tcp.html#SSL-CERTIFICATE-CREATION.
> But the private key is not encrypted.
>
> I noticed in psql 11+ version, a new configuration
> *ssl_passphrase_command* is added, so that encrypted private key can be
> used.
>
> But as far as I know, encrypted private key is not supported in stream
> replication.
>
>
>
> I wonder if there is another way to authenticate in replication? Or does
> pgsql has any plan to support encrypted private key in replication?
>
>
>
>
>
> PostgreSQL replication supports all authentication methods that
> PostgeSQL supports for regular connections, in general. While I haven't
> tried it, ssl_passphrase_command should work for this as well as long as it
> doesn't require manual user interaction. But it could for example read the
> passphrase from a pipe where it's provided off,or from a hardware device.
> Do keep in mind that replication might need multiple authentications (for
> example if the network disconnects, it has to reconnect).
>
>
>
> You can also use for example GSSAPI and Kerberos to do the login. You will
> then of course have to figure out how to securely authenticate the postgres
> OS user on the standby node to the Kerberos system, but that's doable.
> (Though I believe most Kerberos implementations also rely on filesystem
> security to protect the tickets, so if you don't trust your filesystem, you
> may have a problem with that -- as well as indeed most other authentication
> systems -- so you'd have to investigate that within the kerberos system).
>
>
>