postgrespro.git / summary / log / commit / refs

commit    87c346a35ee869e401e736163ec9d21632cc3b0d
Author:   Michael Paquier <michael@paquier.xyz>
Date:     Thu Feb 28 00:40:28 2019 +0000

    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
 			{
 				/*


[parent: da35d1480624]