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

configure

@@ -13092,6 +13092,18 @@ 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

@@ -1316,6 +1316,8 @@ 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])

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

@@ -1313,7 +1313,7 @@ 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)
 {
@@ -1331,10 +1331,15 @@ 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

@@ -301,7 +301,7 @@ 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

@@ -721,6 +721,9 @@
 /* Define to 1 if you have the `writev' function. */
 #undef HAVE_WRITEV
 
+/* 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

@@ -371,7 +371,7 @@ 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)
 {
@@ -391,10 +391,15 @@ 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
 	{
 		appendPQExpBufferStr(&conn->errorMessage,
 							 libpq_gettext("could not determine server certificate signature algorithm\n"));

src/interfaces/libpq/libpq-int.h

@@ -787,7 +787,7 @@ 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/tools/msvc/Solution.pm

@@ -434,6 +434,7 @@ sub GenerateFiles
 		HAVE_WCTYPE_H                            => 1,
 		HAVE_WRITEV                              => 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,
@@ -549,7 +550,14 @@ 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'))
 		{