Re: [HACKERS] Authentication tests, and plain 'password' authentication with a SCRAM verifier

[Heikki Linnakangas]

On 03/14/2017 09:25 PM, Heikki Linnakangas wrote:

On 03/14/2017 09:02 PM, Jeff Janes wrote:

The message returned to the client for the wrong password differs between
pg_hba-set scram and pg_hba-set md5/password methods.  Is that OK?

psql: error received from server in SASL exchange: invalid-proof

psql: FATAL:  password authentication failed for user "test"


Ah yeah, I was on the fence on that one. Currently, the server returns
the invalid-proof error to the client, as defined in RFC5802. That
results in that error message from libpq. Alternatively, the server
could elog(FATAL), like the other authentication mechanisms do, with the
same message. The RFC allows that behavior too but returning the
invalid-proof error code is potentially more friendly to 3rd party SCRAM
implementations.

One option would be to recognize the "invalid-proof" message in libpq,
and construct a more informative error message in libpq. Could use the
same wording, "password authentication failed", but it would behave
differently wrt. translation, at least.


I went ahead and changed the backend code to not send the 
"invalid-proof" error. That seemed like the easiest fix for this. You 
now get the same "password authentication failed" error as with MD5 and 
plain password authentication.


- Heikki



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Re: [HACKERS] Authentication tests, and plain 'password' authentication with a SCRAM verifier

[Heikki Linnakangas]

On 03/14/2017 09:02 PM, Jeff Janes wrote:

It is somewhat disconcerting that the client will send a plain-text
password to a mis-configured (or mal-configured) server, but I don't
think there is anything this patch series can reasonably do about
that.


Yeah. That's one pretty glaring hole with libpq: there's no option to 
disallow insecure authentication mechanisms. That's not new, but now 
that we have SCRAM that's otherwise more secure, it looks worse in 
comparison.


SCRAM also has a nice feature that it provides proof to the client, that 
the server knew the password (or rather, had a verifier for that 
password). In other words, the client knows that it connected to the 
correct server, not a fake one. But currently nothing prevents a fake 
server from simply not doing SCRAM authentication.


We clearly need something similar to sslmode=require in libpq, to 
tighten that up.



The message returned to the client for the wrong password differs between
pg_hba-set scram and pg_hba-set md5/password methods.  Is that OK?

psql: error received from server in SASL exchange: invalid-proof

psql: FATAL:  password authentication failed for user "test"


Ah yeah, I was on the fence on that one. Currently, the server returns 
the invalid-proof error to the client, as defined in RFC5802. That 
results in that error message from libpq. Alternatively, the server 
could elog(FATAL), like the other authentication mechanisms do, with the 
same message. The RFC allows that behavior too but returning the 
invalid-proof error code is potentially more friendly to 3rd party SCRAM 
implementations.


One option would be to recognize the "invalid-proof" message in libpq, 
and construct a more informative error message in libpq. Could use the 
same wording, "password authentication failed", but it would behave 
differently wrt. translation, at least.


- Heikki



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Re: [HACKERS] Authentication tests, and plain 'password' authentication with a SCRAM verifier

[Jeff Janes]

On Tue, Mar 14, 2017 at 5:36 AM, Heikki Linnakangas  wrote:

> Hi,
>
> I didn't include the authentication TAP tests that Michael wrote in the
> main SCRAM commit last week. The main issue was that the new test was
> tacked on the src/test/recovery test suite, for lack of a better place. I
> propose that we add a whole new src/test/authentication directory for it.
> It would also be logical to merge src/test/ssl into it, but the SSL test
> suite has some complicated setup steps, to create the certificates, and it
> cannot be safely run on a multi-user system. So probably best to keep it
> separate, after all.
>
> While looking at the test, I noticed that the SCRAM patch didn't include
> support for logging in with plain 'password' authentication, when the user
> has a SCRAM verifier stored in pg_authid. That was an oversight. If the
> client gives the server the plain password, it's easy for the server to
> verify that it matches the SCRAM verifier.
>

I noticed the asymmetry over plain-text passwords, and didn't know if it
was intentional or not.  It is somewhat disconcerting that the client will
send a plain-text password to a mis-configured (or mal-configured) server,
but I don't think there is anything this patch series can reasonably do
about that.


>
> Attached patches add the TAP test suite, and implement plain 'password'
> authentication for users with SCRAM verifier. Any comments?


Does what it says, says what it does.  There is no installcheck target,
which makes sense because it inherently has to muck around with
pg_hba.conf.  The test should be updated to test the syntax for
0001-Add-clause-PASSWORD-val-USING-protocol-to-CREATE-ALT.patch if that
gets committed.

The message returned to the client for the wrong password differs between
pg_hba-set scram and pg_hba-set md5/password methods.  Is that OK?

psql: error received from server in SASL exchange: invalid-proof

psql: FATAL:  password authentication failed for user "test"

Cheers,

Jeff

[HACKERS] Authentication tests, and plain 'password' authentication with a SCRAM verifier

[Heikki Linnakangas]

Hi,

I didn't include the authentication TAP tests that Michael wrote in the 
main SCRAM commit last week. The main issue was that the new test was 
tacked on the src/test/recovery test suite, for lack of a better place. 
I propose that we add a whole new src/test/authentication directory for 
it. It would also be logical to merge src/test/ssl into it, but the SSL 
test suite has some complicated setup steps, to create the certificates, 
and it cannot be safely run on a multi-user system. So probably best to 
keep it separate, after all.


While looking at the test, I noticed that the SCRAM patch didn't include 
support for logging in with plain 'password' authentication, when the 
user has a SCRAM verifier stored in pg_authid. That was an oversight. If 
the client gives the server the plain password, it's easy for the server 
to verify that it matches the SCRAM verifier.


Attached patches add the TAP test suite, and implement plain 'password' 
authentication for users with SCRAM verifier. Any comments?


- Heikki



0001-Allow-plaintext-password-authentication-when-user-ha.patch
Description: application/download


0002-Add-TAP-tests-for-password-based-authentication-meth.patch
Description: application/download

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