From 87c346a35ee869e401e736163ec9d21632cc3b0d Mon Sep 17 00:00:00 2001 From: Michael Paquier Date: Thu, 28 Feb 2019 09:40:28 +0900 Subject: [PATCH] Fix SCRAM authentication via SSL when mixing versions of OpenSSL 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 --- src/interfaces/libpq/fe-auth.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/src/interfaces/libpq/fe-auth.c b/src/interfaces/libpq/fe-auth.c index 08a5a9c1f3..4cbe64ceb5 100644 --- a/src/interfaces/libpq/fe-auth.c +++ b/src/interfaces/libpq/fe-auth.c @@ -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 { /*