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Fix SCRAM authentication via SSL when mixing versions of OpenSSL

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When using a libpq client linked with OpenSSL 1.0.1 or older to connect
to a backend linked with OpenSSL 1.0.2 or newer, the server would send
SCRAM-SHA-256-PLUS and SCRAM-SHA-256 as valid mechanisms for the SASL
exchange, and the client would choose SCRAM-SHA-256-PLUS even if it does
not support channel binding, leading to a confusing error.  In this
case, what the client ought to do is switch to SCRAM-SHA-256 so as the
authentication can move on and succeed.

So for a SCRAM authentication over SSL, here are all the cases present
and how we deal with them using libpq:
1) Server supports channel binding, it sends SCRAM-SHA-256-PLUS and
SCRAM-SHA-256 as allowed mechanisms.
1-1) Client supports channel binding, chooses SCRAM-SHA-256-PLUS.
1-2) Client does not support channel binding, chooses SCRAM-SHA-256.
2) Server does not support channel binding, sends SCRAM-SHA-256 as
allowed mechanism.
2-1) Client supports channel binding, still it has no choice but to
choose SCRAM-SHA-256.
2-2) Client does not support channel binding, it chooses SCRAM-SHA-256.
In all these scenarios the connection should succeed, and the one which
was handled incorrectly prior this commit is 1-2), causing the
connection attempt to fail because client chose SCRAM-SHA-256-PLUS over
SCRAM-SHA-256.

Reported-by: Hugh Ranalli
Diagnosed-by: Peter Eisentraut
Author: Michael Paquier
Reviewed-by: Peter Eisentraut
Discussion: https://postgr.es/m/CAAhbUMO89SqUk-5mMY+OapgWf-twF2NA5sCucbHEzMfGbvcepA@mail.gmail.com
Backpatch-through: 11
This commit is contained in:
Michael Paquier 2019-02-28 09:40:39 +09:00
parent 50ae619035
commit d9bba27c8b
1 changed files with 13 additions and 3 deletions
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16
src/interfaces/libpq/fe-auth.c
View File

@ -526,14 +526,24 @@ pg_SASL_init(PGconn *conn, int payloadlen)
/*
* Select the mechanism to use. Pick SCRAM-SHA-256-PLUS over anything
* else if a channel binding type is set. Pick SCRAM-SHA-256 if
* nothing else has already been picked. If we add more mechanisms, a
* more refined priority mechanism might become necessary.
* else if a channel binding type is set and if the client supports
* it. Pick SCRAM-SHA-256 if nothing else has already been picked. If
* we add more mechanisms, a more refined priority mechanism might
* become necessary.
*/
if (strcmp(mechanism_buf.data, SCRAM_SHA_256_PLUS_NAME) == 0)
{
if (conn->ssl_in_use)
{
/*
* The server has offered SCRAM-SHA-256-PLUS, which is only
* supported by the client if a hash of the peer certificate
* can be created.
*/
#ifdef HAVE_PGTLS_GET_PEER_CERTIFICATE_HASH
selected_mechanism = SCRAM_SHA_256_PLUS_NAME;
#endif
}
else
{
/*