xz: Add support for OpenBSD's pledge() sandbox.

configure.ac

@@ -523,7 +523,8 @@ AM_CONDITIONAL([COND_SYMVERS_GENERIC],
 
 AC_MSG_CHECKING([if sandboxing should be used])
 AC_ARG_ENABLE([sandbox], [AS_HELP_STRING([--enable-sandbox=METHOD],
-		[Sandboxing METHOD can be `auto', `no', or `capsicum'.
+		[Sandboxing METHOD can be
+		`auto', `no', `capsicum', or `pledge'.
 		The default is `auto' which enables sandboxing if
 		a supported sandboxing method is found.])],
 	[], [enable_sandbox=auto])
@@ -531,12 +532,12 @@ case $enable_sandbox in
 	auto)
 		AC_MSG_RESULT([maybe (autodetect)])
 		;;
-	no | capsicum)
+	no | capsicum | pledge)
 		AC_MSG_RESULT([$enable_sandbox])
 		;;
 	*)
 		AC_MSG_RESULT([])
-		AC_MSG_ERROR([--enable-sandbox only accepts `auto', `no', or `capsicum'.])
+		AC_MSG_ERROR([--enable-sandbox only accepts `auto', `no', `capsicum', or `pledge'.])
 		;;
 esac
 
@@ -816,6 +817,11 @@ case $enable_sandbox in
 		AX_CHECK_CAPSICUM([enable_sandbox=found], [:])
 		;;
 esac
+case $enable_sandbox in
+	auto | pledge)
+		AC_CHECK_FUNCS([pledge], [enable_sandbox=found ; break])
+		;;
+esac
 
 # If a specific sandboxing method was explicitly requested and it wasn't
 # found, give an error.

src/xz/file_io.c

@@ -212,6 +212,17 @@ io_sandbox_enter(int src_fd)
 	if (cap_enter())
 		goto error;
 
+#elif defined(HAVE_PLEDGE)
+	// pledge() was introduced in OpenBSD 5.9.
+	//
+	// main() unconditionally calls pledge() with fairly relaxed
+	// promises which work in all situations. Here we make the
+	// sandbox more strict.
+	if (pledge("stdio", ""))
+		goto error;
+
+	(void)src_fd;
+
 #else
 #	error ENABLE_SANDBOX is defined but no sandboxing method was found.
 #endif

src/xz/main.c

@@ -163,6 +163,19 @@ main(int argc, char **argv)
 	// on the command line, thus this must be done before args_parse().
 	hardware_init();
 
+#ifdef HAVE_PLEDGE
+	// OpenBSD's pledge() sandbox
+	//
+	// Unconditionally enable sandboxing with fairly relaxed promises.
+	// This is still way better than having no sandbox at all. :-)
+	// More strict promises will be made later in file_io.c if possible.
+	//
+	// This is done only after the above initializations
+	// as the error message needs locale support.
+	if (pledge("stdio rpath wpath cpath fattr", ""))
+		message_fatal(_("Failed to enable the sandbox"));
+#endif
+
 	// Parse the command line arguments and get an array of filenames.
 	// This doesn't return if something is wrong with the command line
 	// arguments. If there are no arguments, one filename ("-") is still

src/xz/private.h

@@ -45,7 +45,7 @@
 #	define STDERR_FILENO (fileno(stderr))
 #endif
 
-#ifdef HAVE_CAPSICUM
+#if defined(HAVE_CAPSICUM) || defined(HAVE_PLEDGE)
 #	define ENABLE_SANDBOX 1
 #endif