Fix sslkeylogfile error handling logging

When sslkeylogfile has been set but the file fails to open in an
otherwise successful connection, the log entry added to the conn
object is never printed.  Instead print the error on stderr for
increased visibility.  This is a debugging tool so using stderr
for logging is appropriate.  Also while there, remove the umask
call in the callback as it's not useful.

Issues noted by Peter Eisentraut in post-commit review, backpatch
down to 18 when support for sslkeylogfile was added

Author: Daniel Gustafsson <daniel@yesql.se>
Reported-by: Peter Eisentraut <peter@eisentraut.org>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://postgr.es/m/70450bee-cfaa-48ce-8980-fc7efcfebb03@eisentraut.org
Backpatch-through: 18

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

@@ -693,34 +693,35 @@ static unsigned char alpn_protos[] = PG_ALPN_PROTOCOL_VECTOR;
  * purposes.  The file will be written using the NSS keylog format.  LibreSSL
  * 3.5 introduced stub function to set the callback for OpenSSL compatibility
  * but the callback is never invoked.
+ *
+ * Error messages added to the connection object wont be printed anywhere if
+ * the connection is successful.  Errors in processing keylogging are printed
+ * to stderr to overcome this.
  */
 static void
 SSL_CTX_keylog_cb(const SSL *ssl, const char *line)
 {
 	int			fd;
-	mode_t		old_umask;
 	ssize_t		rc;
 	PGconn	   *conn = SSL_get_app_data(ssl);
 
 	if (conn == NULL)
 		return;
 
-	old_umask = umask(077);
 	fd = open(conn->sslkeylogfile, O_WRONLY | O_APPEND | O_CREAT, 0600);
-	umask(old_umask);
 
 	if (fd == -1)
 	{
-		libpq_append_conn_error(conn, "could not open SSL key logging file \"%s\": %s",
-								conn->sslkeylogfile, pg_strerror(errno));
+		fprintf(stderr, libpq_gettext("WARNING: could not open SSL key logging file \"%s\": %m\n"),
+				conn->sslkeylogfile);
 		return;
 	}
 
 	/* line is guaranteed by OpenSSL to be NUL terminated */
 	rc = write(fd, line, strlen(line));
 	if (rc < 0)
-		libpq_append_conn_error(conn, "could not write to SSL key logging file \"%s\": %s",
-								conn->sslkeylogfile, pg_strerror(errno));
+		fprintf(stderr, libpq_gettext("WARNING: could not write to SSL key logging file \"%s\": %m\n"),
+				conn->sslkeylogfile);
 	else
 		rc = write(fd, "\n", 1);
 	(void) rc;					/* silence compiler warnings */
@@ -1044,6 +1045,10 @@ initialize_SSL(PGconn *conn)
 	}
 	conn->ssl_in_use = true;
 
+	/*
+	 * If SSL key logging is requested, set up the callback if a compatible
+	 * version of OpenSSL is used and libpq was compiled to support it.
+	 */
 	if (conn->sslkeylogfile && strlen(conn->sslkeylogfile) > 0)
 	{
 #ifdef HAVE_SSL_CTX_SET_KEYLOG_CALLBACK
@@ -1057,7 +1062,6 @@ initialize_SSL(PGconn *conn)
 #endif
 	}
 
-
 	/*
 	 * SSL contexts are reference counted by OpenSSL. We can free it as soon
 	 * as we have created the SSL object, and it will stick around for as long

src/test/ssl/t/001_ssltests.pl

@@ -173,6 +173,13 @@ SKIP:
 	ok( (@status = stat("$tempdir/key.txt")),
 		"keylog file exists and returned status");
 	ok(@status && !($status[2] & 0006), "keylog file is not world readable");
+
+	# Connect should work with an incorrect sslkeylogfile, with the error to
+	# open the logfile printed to stderr
+	$node->connect_ok(
+		"$common_connstr sslrootcert=ssl/root+server_ca.crt sslkeylogfile=$tempdir/invalid/key.txt sslmode=require",
+		"connect with server root cert and incorrect sslkeylogfile path",
+		expected_stderr => qr/could not open/);
 }
 
 # The server should not accept non-SSL connections.