Fix handling of SCRAM-SHA-256's channel binding with RSA-PSS certificates

OpenSSL 1.1.1 and newer versions have added support for RSA-PSS
certificates, which requires the use of a specific routine in OpenSSL to
determine which hash function to use when compiling it when using
channel binding in SCRAM-SHA-256.  X509_get_signature_nid(), that is the
original routine the channel binding code has relied on, is not able to
determine which hash algorithm to use for such certificates.  However,
X509_get_signature_info(), new to OpenSSL 1.1.1, is able to do it.  This
commit switches the channel binding logic to rely on
X509_get_signature_info() over X509_get_signature_nid(), which would be
the choice when building with 1.1.1 or newer.

The error could have been triggered on the client or the server, hence
libpq and the backend need to have their related code paths patched.
Note that attempting to load an RSA-PSS certificate with OpenSSL 1.1.0
or older leads to a failure due to an unsupported algorithm.

The discovery of relying on X509_get_signature_info() comes from Jacob,
the tests have been written by Heikki (with few tweaks from me), while I
have bundled the whole together while adding the bits needed for MSVC
and meson.

This issue exists since channel binding exists, so backpatch all the way
down.  Some tests are added in 15~, triggered if compiling with OpenSSL
1.1.1 or newer, where the certificate and key files can easily be
generated for RSA-PSS.

Reported-by: Gunnar "Nick" Bluth
Author: Jacob Champion, Heikki Linnakangas
Discussion: https://postgr.es/m/17760-b6c61e752ec07060@postgresql.org
Backpatch-through: 11

Author: michaelpq

configure

@@ -13013,6 +13013,18 @@ if test "x$ac_cv_func_CRYPTO_lock" = xyes; then :
 #define HAVE_CRYPTO_LOCK 1
 _ACEOF
 
+fi
+done
+
+  # Function introduced in OpenSSL 1.1.1.
+  for ac_func in X509_get_signature_info
+do :
+  ac_fn_c_check_func "$LINENO" "X509_get_signature_info" "ac_cv_func_X509_get_signature_info"
+if test "x$ac_cv_func_X509_get_signature_info" = xyes; then :
+  cat >>confdefs.h <<_ACEOF
+#define HAVE_X509_GET_SIGNATURE_INFO 1
+_ACEOF
+
 fi
 done
 

configure.ac

@@ -1385,6 +1385,8 @@ if test "$with_ssl" = openssl ; then
   # thread-safety. In 1.1.0, it's no longer required, and CRYPTO_lock()
   # function was removed.
   AC_CHECK_FUNCS([CRYPTO_lock])
+  # Function introduced in OpenSSL 1.1.1.
+  AC_CHECK_FUNCS([X509_get_signature_info])
   AC_DEFINE([USE_OPENSSL], 1, [Define to 1 to build with OpenSSL support. (--with-ssl=openssl)])
 elif test "$with_ssl" != no ; then
   AC_MSG_ERROR([--with-ssl must specify openssl])

meson.build

@@ -1223,6 +1223,9 @@ if get_option('ssl') == 'openssl'
     # thread-safety. In 1.1.0, it's no longer required, and CRYPTO_lock()
     # function was removed.
     ['CRYPTO_lock'],
+
+    # Function introduced in OpenSSL 1.1.1
+    ['X509_get_signature_info'],
   ]
 
   foreach c : check_funcs

src/backend/libpq/be-secure-openssl.c

@@ -1429,7 +1429,7 @@ be_tls_get_peer_serial(Port *port, char *ptr, size_t len)
 		ptr[0] = '\0';
 }
 
-#ifdef HAVE_X509_GET_SIGNATURE_NID
+#if defined(HAVE_X509_GET_SIGNATURE_NID) || defined(HAVE_X509_GET_SIGNATURE_INFO)
 char *
 be_tls_get_certificate_hash(Port *port, size_t *len)
 {
@@ -1447,10 +1447,15 @@ be_tls_get_certificate_hash(Port *port, size_t *len)
 
 	/*
 	 * Get the signature algorithm of the certificate to determine the hash
-	 * algorithm to use for the result.
+	 * algorithm to use for the result.  Prefer X509_get_signature_info(),
+	 * introduced in OpenSSL 1.1.1, which can handle RSA-PSS signatures.
 	 */
+#if HAVE_X509_GET_SIGNATURE_INFO
+	if (!X509_get_signature_info(server_cert, &algo_nid, NULL, NULL, NULL))
+#else
 	if (!OBJ_find_sigid_algs(X509_get_signature_nid(server_cert),
 							 &algo_nid, NULL))
+#endif
 		elog(ERROR, "could not determine server certificate signature algorithm");
 
 	/*

src/include/libpq/libpq-be.h

@@ -308,7 +308,7 @@ extern void be_tls_get_peer_serial(Port *port, char *ptr, size_t len);
  * This is not supported with old versions of OpenSSL that don't have
  * the X509_get_signature_nid() function.
  */
-#if defined(USE_OPENSSL) && defined(HAVE_X509_GET_SIGNATURE_NID)
+#if defined(USE_OPENSSL) && (defined(HAVE_X509_GET_SIGNATURE_NID) || defined(HAVE_X509_GET_SIGNATURE_INFO))
 #define HAVE_BE_TLS_GET_CERTIFICATE_HASH
 extern char *be_tls_get_certificate_hash(Port *port, size_t *len);
 #endif

src/include/pg_config.h.in

@@ -523,6 +523,9 @@
 /* Define to 1 if you have the `wcstombs_l' function. */
 #undef HAVE_WCSTOMBS_L
 
+/* Define to 1 if you have the `X509_get_signature_info' function. */
+#undef HAVE_X509_GET_SIGNATURE_INFO
+
 /* Define to 1 if you have the `X509_get_signature_nid' function. */
 #undef HAVE_X509_GET_SIGNATURE_NID
 

src/interfaces/libpq/fe-secure-openssl.c

@@ -364,7 +364,7 @@ pgtls_write(PGconn *conn, const void *ptr, size_t len)
 	return n;
 }
 
-#ifdef HAVE_X509_GET_SIGNATURE_NID
+#if defined(HAVE_X509_GET_SIGNATURE_NID) || defined(HAVE_X509_GET_SIGNATURE_INFO)
 char *
 pgtls_get_peer_certificate_hash(PGconn *conn, size_t *len)
 {
@@ -384,10 +384,15 @@ pgtls_get_peer_certificate_hash(PGconn *conn, size_t *len)
 
 	/*
 	 * Get the signature algorithm of the certificate to determine the hash
-	 * algorithm to use for the result.
+	 * algorithm to use for the result.  Prefer X509_get_signature_info(),
+	 * introduced in OpenSSL 1.1.1, which can handle RSA-PSS signatures.
 	 */
+#if HAVE_X509_GET_SIGNATURE_INFO
+	if (!X509_get_signature_info(peer_cert, &algo_nid, NULL, NULL, NULL))
+#else
 	if (!OBJ_find_sigid_algs(X509_get_signature_nid(peer_cert),
 							 &algo_nid, NULL))
+#endif
 	{
 		libpq_append_conn_error(conn, "could not determine server certificate signature algorithm");
 		return NULL;

src/interfaces/libpq/libpq-int.h

@@ -806,7 +806,7 @@ extern ssize_t pgtls_write(PGconn *conn, const void *ptr, size_t len);
  * This is not supported with old versions of OpenSSL that don't have
  * the X509_get_signature_nid() function.
  */
-#if defined(USE_OPENSSL) && defined(HAVE_X509_GET_SIGNATURE_NID)
+#if defined(USE_OPENSSL) && (defined(HAVE_X509_GET_SIGNATURE_NID) || defined(HAVE_X509_GET_SIGNATURE_INFO))
 #define HAVE_PGTLS_GET_PEER_CERTIFICATE_HASH
 extern char *pgtls_get_peer_certificate_hash(PGconn *conn, size_t *len);
 #endif

src/test/ssl/README

@@ -92,6 +92,7 @@ ssl/ subdirectory. The Makefile also contains a rule, "make sslfiles", to
 recreate them if you need to make changes. "make sslfiles-clean" is required
 in order to recreate the full set of keypairs and certificates. To rebuild
 separate files, touch (or remove) the files in question and run "make sslfiles".
+This step requires at least OpenSSL 1.1.1.
 
 Note
 ====

src/test/ssl/conf/server-rsapss.config

@@ -0,0 +1,14 @@
+# An OpenSSL format CSR config file for creating a server certificate.
+#
+# This is identical to server-cn-only certificate, but we specify
+# RSA-PSS as the algorithm on the command line.
+
+[ req ]
+distinguished_name     = req_distinguished_name
+prompt                 = no
+
+[ req_distinguished_name ]
+CN = common-name.pg-ssltest.test
+OU = PostgreSQL test suite
+
+# No Subject Alternative Names

src/test/ssl/ssl/server-rsapss.crt

@@ -0,0 +1,21 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----

src/test/ssl/ssl/server-rsapss.key

@@ -0,0 +1,28 @@
+-----BEGIN PRIVATE KEY-----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+-----END PRIVATE KEY-----

src/test/ssl/sslfiles.mk

@@ -37,13 +37,17 @@ CLIENTS := client client-dn client-revoked client_ext client-long \
 	client-revoked-utf8
 
 #
-# To add a new non-standard key, add it to SPECIAL_KEYS and then add a recipe
-# for creating it to the "Special-case keys" section below.
+# To add a new non-standard certificate, add it to SPECIAL_CERTS and then add
+# a recipe for creating it to the "Special-case certificates" section below.
 #
+SPECIAL_CERTS := ssl/server-rsapss.crt
+
+# Likewise for non-standard keys
 SPECIAL_KEYS := ssl/server-password.key \
 	ssl/client-der.key \
 	ssl/client-encrypted-pem.key \
-	ssl/client-encrypted-der.key
+	ssl/client-encrypted-der.key \
+	ssl/server-rsapss.key
 
 #
 # These files are just concatenations of other files. You can add new ones to
@@ -66,7 +70,13 @@ CRLS := ssl/root.crl \
 	ssl/client.crl \
 	ssl/server.crl
 
-SSLFILES := $(STANDARD_CERTS) $(STANDARD_KEYS) $(SPECIAL_KEYS) $(COMBINATIONS) $(CRLS)
+SSLFILES := \
+	$(STANDARD_CERTS) \
+	$(STANDARD_KEYS) \
+	$(SPECIAL_CERTS) \
+	$(SPECIAL_KEYS) \
+	$(COMBINATIONS) \
+	$(CRLS)
 SSLDIRS := ssl/client-crldir \
 	ssl/server-crldir \
 	ssl/root+client-crldir \
@@ -86,6 +96,10 @@ sslfiles: $(SSLFILES) $(SSLDIRS)
 ssl/root_ca.crt: ssl/root_ca.key conf/root_ca.config
 	$(OPENSSL) req -new -x509 -config conf/root_ca.config -days 10000 -key $< -out $@
 
+# Certificate using RSA-PSS algorithm. Also self-signed.
+ssl/server-rsapss.crt: ssl/server-rsapss.key conf/server-rsapss.config
+	$(OPENSSL) req -new -x509 -config conf/server-rsapss.config -key $< -out $@
+
 #
 # Special-case keys
 #
@@ -96,6 +110,10 @@ ssl/root_ca.crt: ssl/root_ca.key conf/root_ca.config
 ssl/server-password.key: ssl/server-cn-only.key
 	$(OPENSSL) rsa -aes256 -in $< -out $@ -passout 'pass:secret1'
 
+# Key that uses the RSA-PSS algorithm
+ssl/server-rsapss.key:
+	$(OPENSSL) genpkey -algorithm rsa-pss -out $@
+
 # DER-encoded version of client.key
 ssl/client-der.key: ssl/client.key
 	$(OPENSSL) rsa -in $< -outform DER -out $@

src/test/ssl/t/002_scram.pl

@@ -46,6 +46,10 @@ sub switch_server_cert
 # Determine whether build supports tls-server-end-point.
 my $supports_tls_server_end_point =
   check_pg_config("#define HAVE_X509_GET_SIGNATURE_NID 1");
+# Determine whether build supports detection of hash algorithms for
+# RSA-PSS certificates.
+my $supports_rsapss_certs =
+  check_pg_config("#define HAVE_X509_GET_SIGNATURE_INFO 1");
 
 # Allocation of base connection string shared among multiple tests.
 my $common_connstr;
@@ -136,4 +140,17 @@ sub switch_server_cert
 		qr/connection authenticated: identity="ssltestuser" method=scram-sha-256/
 	]);
 
+# Now test with a server certificate that uses the RSA-PSS algorithm.
+# This checks that the certificate can be loaded and that channel binding
+# works. (see bug #17760)
+if ($supports_rsapss_certs)
+{
+	switch_server_cert($node, certfile => 'server-rsapss');
+	$node->connect_ok(
+		"$common_connstr user=ssltestuser channel_binding=require",
+		"SCRAM with SSL and channel_binding=require, server certificate uses 'rsassaPss'",
+		log_like => [
+			qr/connection authenticated: identity="ssltestuser" method=scram-sha-256/
+		]);
+}
 done_testing();

src/tools/msvc/Solution.pm

@@ -371,6 +371,7 @@ sub GenerateFiles
 		HAVE_WCSTOMBS_L                          => 1,
 		HAVE_VISIBILITY_ATTRIBUTE                => undef,
 		HAVE_X509_GET_SIGNATURE_NID              => 1,
+		HAVE_X509_GET_SIGNATURE_INFO             => undef,
 		HAVE_X86_64_POPCNTQ                      => undef,
 		HAVE__BOOL                               => undef,
 		HAVE__BUILTIN_BSWAP16                    => undef,
@@ -489,7 +490,14 @@ sub GenerateFiles
 
 		my ($digit1, $digit2, $digit3) = $self->GetOpenSSLVersion();
 
-		# More symbols are needed with OpenSSL 1.1.0 and above.
+		# Symbols needed with OpenSSL 1.1.1 and above.
+		if (   ($digit1 >= '3' && $digit2 >= '0' && $digit3 >= '0')
+			|| ($digit1 >= '1' && $digit2 >= '1' && $digit3 >= '1'))
+		{
+			$define{HAVE_X509_GET_SIGNATURE_INFO} = 1;
+		}
+
+		# Symbols needed with OpenSSL 1.1.0 and above.
 		if (   ($digit1 >= '3' && $digit2 >= '0' && $digit3 >= '0')
 			|| ($digit1 >= '1' && $digit2 >= '1' && $digit3 >= '0'))
 		{