Use closefrom() to not loop over all possible file descriptors

Resolves: https://gitlab.freedesktop.org/dbus/dbus/-/issues/278

cmake/ConfigureChecks.cmake

@@ -52,6 +52,7 @@ check_symbol_exists(getpwnam_r   "errno.h;pwd.h"    HAVE_GETPWNAM_R)         #
 check_symbol_exists(setenv       "stdlib.h"         HAVE_SETENV)             #  dbus-sysdeps.c
 check_symbol_exists(unsetenv     "stdlib.h"         HAVE_UNSETENV)           #  dbus-sysdeps.c
 check_symbol_exists(clearenv     "stdlib.h"         HAVE_CLEARENV)           #  dbus-sysdeps.c
+check_symbol_exists(closefrom    "unistd.h"         HAVE_CLOSEFROM)          #  dbus-sysdeps-unix.c
 check_symbol_exists(writev       "sys/uio.h"        HAVE_WRITEV)             #  dbus-sysdeps.c, dbus-sysdeps-win.c
 check_symbol_exists(setrlimit    "sys/resource.h"   HAVE_SETRLIMIT)          #  dbus-sysdeps.c, dbus-sysdeps-win.c, test/test-segfault.c
 check_symbol_exists(socketpair   "sys/socket.h"     HAVE_SOCKETPAIR)         #  dbus-sysdeps.c

cmake/config.h.cmake

@@ -201,6 +201,9 @@
 /* Define to 1 if you have clearenv */
 #cmakedefine   HAVE_CLEARENV 1
 
+/* Define to 1 if you have closefrom */
+#cmakedefine   HAVE_CLOSEFROM 1
+
 /* Define to 1 if you have writev */
 #cmakedefine   HAVE_WRITEV 1
 

configure.ac

@@ -382,6 +382,7 @@ AS_IF([test x$enable_code_coverage = xyes],[
 AC_CHECK_FUNCS_ONCE([
 accept4
 clearenv
+closefrom
 fpathconf
 getgrouplist
 getpeereid

dbus/dbus-sysdeps-unix.c

@@ -4796,7 +4796,11 @@ act_on_fds_3_and_up (void (*func) (int fd))
 void
 _dbus_close_all (void)
 {
+#ifdef HAVE_CLOSEFROM
+  closefrom (3);
+#else
   act_on_fds_3_and_up (close_ignore_error);
+#endif
 }
 
 /**