Commit e7b84ca4 authored by Hans de Goede's avatar Hans de Goede

Xorg: Add a suid root wrapper

With the recent systemd-logind changes it is possible to install the Xorg
binary without suid root rights and still have everything working as it
should *if* the user only has cards which are supported by kms.

This commit adds a little suid root wrapper, which is a bit weird, first we
strip the suid-root bit of the Xorg binary, and then we add a wrapper ?

The function of this wrapper is to see if a system still needs root-rights,
if it does not (it supports kms and the kms drivers are properly loaded),
then it will immediately drop all elevated rights before executing the real
Xorg binary. If it finds (some) cards which don't support kms, or no cards
at all, then it will execute the Xorg server with elevated rights so that
ie the nvidia binary driver and the vesa driver can keep working normally.

To make it possible for security concious users who don't need the root
rights to completely remove the wrapper, Xorg is started in a 3 step process
when the wrapper is enabled during build time:

1) A simple shell script which checks if the wrapper is there, if it is
  it executes the wrapper, if not it directly executes the real Xorg binary

2) The wrapper gets executed, does its checks, normally drops all elevated
  rights and then executes the real Xorg binary

3) The real Xorg binary does its thing

This allows distributions to put the wrapper binary in a separate package, and
will allow users to remove this package. IE the plan with Fedora is to make
"legacy" drivers depend on the wrapper pkg, and since our default install
contains some legacy drivers it will be part of the default install, but
users can later yum remove it (which will also automatically remove the
legacy driver packages as those won't work without it anyways).

The wrapper is loosely modelled after the existing Debian Xwrapper, it
uses the same config-file + config-file format, and also allows restricting
Xserver execution (through the wrapper) to console users only.

There also is a new needs_root_rights config file directive, which can
be used to override the auto-detection the wrapper does.

Hopefully this will allow Debian to replace their own wrapper with this
upstream one.
Signed-off-by: default avatarHans de Goede <hdegoede@redhat.com>
Reviewed-by: Peter Hutterer's avatarPeter Hutterer <peter.hutterer@who-t.net>
parent 81a4952d
......@@ -627,6 +627,7 @@ AC_ARG_ENABLE(pciaccess, AS_HELP_STRING([--enable-pciaccess], [Build Xorg with p
AC_ARG_ENABLE(linux_acpi, AS_HELP_STRING([--disable-linux-acpi], [Disable building ACPI support on Linux (if available).]), [enable_linux_acpi=$enableval], [enable_linux_acpi=yes])
AC_ARG_ENABLE(linux_apm, AS_HELP_STRING([--disable-linux-apm], [Disable building APM support on Linux (if available).]), [enable_linux_apm=$enableval], [enable_linux_apm=yes])
AC_ARG_ENABLE(systemd-logind, AC_HELP_STRING([--enable-systemd-logind], [Build systemd-logind support (default: auto)]), [SYSTEMD_LOGIND=$enableval], [SYSTEMD_LOGIND=auto])
AC_ARG_ENABLE(suid-wrapper, AC_HELP_STRING([--enable-suid-wrapper], [Build suid-root wrapper for legacy driver support on rootless xserver systems (default: no)]), [SUID_WRAPPER=$enableval], [SUID_WRAPPER=no])
dnl DDXes.
AC_ARG_ENABLE(xorg, AS_HELP_STRING([--enable-xorg], [Build Xorg server (default: auto)]), [XORG=$enableval], [XORG=auto])
......@@ -924,6 +925,16 @@ if test "x$SYSTEMD_LOGIND" = xyes; then
fi
AM_CONDITIONAL(SYSTEMD_LOGIND, [test "x$SYSTEMD_LOGIND" = xyes])
if test "x$SUID_WRAPPER" = xyes; then
dnl The wrapper uses libdrm headers, so ensure they are available
PKG_CHECK_MODULES([LIBDRM], $LIBDRM)
dnl This is a define so that if some platforms want to put the wrapper
dnl somewhere else this can be easily changed
AC_DEFINE_DIR(SUID_WRAPPER_DIR, libexecdir, [Where to install Xorg.bin and Xorg.wrap])
SETUID="no"
fi
AM_CONDITIONAL(SUID_WRAPPER, [test "x$SUID_WRAPPER" = xyes])
if test "x$NEED_DBUS" = xyes; then
AC_DEFINE(NEED_DBUS, 1, [Enable D-Bus core])
fi
......@@ -2116,7 +2127,6 @@ fi
AC_MSG_RESULT([$XWIN])
if test "x$XWIN" = xyes; then
AC_DEFINE_DIR(SYSCONFDIR, sysconfdir, [Location of system.XWinrc])
AC_DEFINE_DIR(DEFAULT_LOGDIR, logdir, [Default log location])
AC_DEFINE_UNQUOTED(XORG_VERSION_CURRENT, [$VENDOR_RELEASE], [Current Xorg version])
AC_DEFINE_UNQUOTED(__VENDORDWEBSUPPORT__, ["$VENDOR_WEB"], [Vendor web address for support])
......@@ -2440,6 +2450,7 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
[ Enable GNU and other extensions to the C environment for glibc])])
AC_DEFINE_DIR(PROJECTROOT, prefix, [Overall prefix])
AC_DEFINE_DIR(SYSCONFDIR, sysconfdir, [sysconfdir])
AC_SUBST([RELEASE_DATE])
BUILD_DATE="`date +'%Y%m%d'`"
......@@ -2499,6 +2510,7 @@ dri3/Makefile
present/Makefile
hw/Makefile
hw/xfree86/Makefile
hw/xfree86/Xorg.sh
hw/xfree86/common/Makefile
hw/xfree86/common/xf86Build.h
hw/xfree86/ddc/Makefile
......
......@@ -81,9 +81,15 @@ Xorg_DEPENDENCIES = $(LOCAL_LIBS)
Xorg_LDFLAGS = $(LD_EXPORT_SYMBOLS_FLAG)
if SUID_WRAPPER
wrapdir = $(SUID_WRAPPER_DIR)
wrap_PROGRAMS = Xorg.wrap
Xorg_wrap_SOURCES = xorg-wrapper.c
endif
BUILT_SOURCES = xorg.conf.example
DISTCLEANFILES = xorg.conf.example
EXTRA_DIST = xorgconf.cpp
EXTRA_DIST = xorgconf.cpp Xorg.sh.in
# Without logdir, X will post an error on the terminal and will not start
install-data-local:
......@@ -98,6 +104,11 @@ if INSTALL_SETUID
chown root $(DESTDIR)$(bindir)/Xorg
chmod u+s $(DESTDIR)$(bindir)/Xorg
endif
if SUID_WRAPPER
mv $(DESTDIR)$(bindir)/Xorg $(DESTDIR)$(SUID_WRAPPER_DIR)/Xorg.bin
${INSTALL} -m 755 Xorg.sh $(DESTDIR)$(bindir)/Xorg
-chown root $(DESTDIR)$(SUID_WRAPPER_DIR)/Xorg.wrap && chmod u+s $(DESTDIR)$(SUID_WRAPPER_DIR)/Xorg.wrap
endif
uninstall-local:
if CYGWIN
......@@ -119,7 +130,7 @@ xorg.conf.example: xorgconf.cpp
relink:
$(AM_V_at)rm -f Xorg$(EXEEXT) && $(MAKE) Xorg$(EXEEXT)
CLEANFILES = sdksyms.c sdksyms.dep
CLEANFILES = sdksyms.c sdksyms.dep Xorg.sh
EXTRA_DIST += sdksyms.sh
sdksyms.dep sdksyms.c: sdksyms.sh
......
#!/bin/sh
#
# Execute Xorg.wrap if it exists otherwise execute Xorg.bin directly.
# This allows distros to put the suid wrapper in a separate package.
basedir=@SUID_WRAPPER_DIR@
if [ -x "$basedir"/Xorg.wrap ]; then
exec "$basedir"/Xorg.wrap "$@"
else
exec "$basedir"/Xorg.bin "$@"
fi
include $(top_srcdir)/manpages.am
appman_PRE = Xorg.man
fileman_PRE = xorg.conf.man xorg.conf.d.man
if SUID_WRAPPER
appman_PRE += Xorg.wrap.man
fileman_PRE += Xwrapper.config.man
endif
.\" Xwrapper.wrap.1
.\"
.\" Copyright 2014 Red Hat, Inc.
.\"
.\" Permission to use, copy, modify, distribute, and sell this software and its
.\" documentation for any purpose is hereby granted without fee, provided that
.\" the above copyright notice appear in all copies and that both that
.\" copyright notice and this permission notice appear in supporting
.\" documentation.
.\"
.\" The above copyright notice and this permission notice shall be included
.\" in all copies or substantial portions of the Software.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
.\" OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
.\" MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
.\" IN NO EVENT SHALL THE OPEN GROUP BE LIABLE FOR ANY CLAIM, DAMAGES OR
.\" OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
.\" ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
.\" OTHER DEALINGS IN THE SOFTWARE.
.\"
.\" Except as contained in this notice, the name of The Open Group shall
.\" not be used in advertising or otherwise to promote the sale, use or
.\" other dealings in this Software without prior written authorization
.\" from The Open Group.
.\"
.\" shorthand for double quote that works everywhere.
.ds q \N'34'
.TH Xorg.wrap 1 __xorgversion__
.SH NAME
Xorg.wrap \- Xorg X server binary wrapper
.SH DESCRIPTION
The Xorg X server may need root rights to function properly. To start the
Xorg X server with these rights your system is using a suid root wrapper
installed as __suid_wrapper_dir__/Xorg.wrap which will execute the real
X server which is installed as __suid_wrapper_dir__/Xorg.bin .
.PP
By default Xorg.wrap will autodetect if root rights are necessary, and
if not it will drop its elevated rights before starting the real X server.
By default Xorg.wrap will only allow executing the real X server from login
sessions on a physical console.
.SH CONFIG FILE
Xorg.wrap's default behavior can be overridden from the
\fI__sysconfdir__/X11/Xwrapper.config\fP config file. Lines starting with a
\fB#\fP in Xwrapper.config are considered comments and will be ignored. Any
other non empty lines must take the form of \fBkey\fP = \fIvalue\fP.
.TP 8
\fBallowed_users\fP = \fIrootonly\fP|\fIconsole\fP|\fIanybody\fP
Specify which users may start the X server through the wrapper. Use
\fIrootonly\fP to only allow root, use \fIconsole\fP to only allow users
logged into a physical console, and use \fIanybody\fP to allow anybody.
The default is \fIconsole\fP.
.TP 8
\fBneeds_root_rights\fP = \fIyes\fP|\fIno\fP|\fIauto\fP
Configure if the wrapper should drop its elevated (root) rights before starting
the X server. Use \fIyes\fP to force execution as root, \fIno\fP to force
execution with all suid rights dropped, and \fIauto\fP to letter the wrapper
auto-detect. The default is \fIauto\fP.
.PP
When auto-detecting the wrapper will drop rights if kms graphics are available
and not drop them if no kms graphics are detected. If a system has multiple
graphics cards and some are not kms capable auto-detection may fail,
in this case manual configuration should be used.
.SH "SEE ALSO"
Xorg X server information: \fIXorg\fP(1)
/*
* Copyright © 2014 Red Hat, Inc.
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice (including the next
* paragraph) shall be included in all copies or substantial portions of the
* Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
* DEALINGS IN THE SOFTWARE.
*
* Author: Hans de Goede <hdegoede@redhat.com>
*/
#include "dix-config.h"
#include <fcntl.h>
#include <limits.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <drm/drm.h>
#include <xf86drm.h> /* For DRM_DEV_NAME */
#define CONFIG_FILE SYSCONFDIR "/X11/Xwrapper.config"
enum { ROOT_ONLY, CONSOLE_ONLY, ANYBODY };
/* KISS non locale / LANG parsing isspace version */
static int is_space(char c)
{
return c == ' ' || c == '\t' || c == '\n';
}
static char *strip(char *s)
{
int i;
/* Strip leading whitespace */
while (s[0] && is_space(s[0]))
s++;
/* Strip trailing whitespace */
i = strlen(s) - 1;
while (i >= 0 && is_space(s[i])) {
s[i] = 0;
i--;
}
return s;
}
static void parse_config(int *allowed, int *needs_root_rights)
{
FILE *f;
char buf[1024];
char *stripped, *equals, *key, *value;
int line = 0;
f = fopen(CONFIG_FILE, "r");
if (!f)
return;
while (fgets(buf, sizeof(buf), f)) {
line++;
/* Skip comments and empty lines */
stripped = strip(buf);
if (stripped[0] == '#' || stripped[0] == 0)
continue;
/* Split in a key + value pair */
equals = strchr(stripped, '=');
if (!equals) {
fprintf(stderr, "Syntax error at %s line %d\n", CONFIG_FILE, line);
exit(1);
}
*equals = 0;
key = strip(stripped); /* To remove trailing whitespace from key */
value = strip(equals + 1); /* To remove leading whitespace from val */
if (!key[0]) {
fprintf(stderr, "Missing key at %s line %d\n", CONFIG_FILE, line);
exit(1);
}
if (!value[0]) {
fprintf(stderr, "Missing value at %s line %d\n", CONFIG_FILE, line);
exit(1);
}
/* And finally process */
if (strcmp(key, "allowed_users") == 0) {
if (strcmp(value, "rootonly") == 0)
*allowed = ROOT_ONLY;
else if (strcmp(value, "console") == 0)
*allowed = CONSOLE_ONLY;
else if (strcmp(value, "anybody") == 0)
*allowed = ANYBODY;
else {
fprintf(stderr,
"Invalid value '%s' for 'allowed_users' at %s line %d\n",
value, CONFIG_FILE, line);
exit(1);
}
}
else if (strcmp(key, "needs_root_rights") == 0) {
if (strcmp(value, "yes") == 0)
*needs_root_rights = 1;
else if (strcmp(value, "no") == 0)
*needs_root_rights = 0;
else if (strcmp(value, "auto") == 0)
*needs_root_rights = -1;
else {
fprintf(stderr,
"Invalid value '%s' for 'needs_root_rights' at %s line %d\n",
value, CONFIG_FILE, line);
exit(1);
}
}
else if (strcmp(key, "nice_value") == 0) {
/* Backward compatibility with older Debian Xwrapper, ignore */
}
else {
fprintf(stderr, "Invalid key '%s' at %s line %d\n", key,
CONFIG_FILE, line);
exit(1);
}
}
fclose(f);
}
int main(int argc, char *argv[])
{
struct drm_mode_card_res res;
struct stat st;
char buf[PATH_MAX];
int i, r, fd;
int kms_cards = 0;
int total_cards = 0;
int allowed = CONSOLE_ONLY;
int needs_root_rights = -1;
parse_config(&allowed, &needs_root_rights);
/* For non root users check if they are allowed to run the X server */
if (getuid() != 0) {
switch (allowed) {
case ROOT_ONLY:
/* Already checked above */
fprintf(stderr, "%s: Only root is allowed to run the X server\n", argv[0]);
exit(1);
break;
case CONSOLE_ONLY:
/* Some of stdin / stdout / stderr maybe redirected to a file */
for (i = STDIN_FILENO; i <= STDERR_FILENO; i++) {
r = fstat(i, &st);
if (r == 0 && S_ISCHR(st.st_mode) && major(st.st_rdev) == 4)
break;
}
if (i > STDERR_FILENO) {
fprintf(stderr, "%s: Only console users are allowed to run the X server\n", argv[0]);
exit(1);
}
break;
case ANYBODY:
break;
}
}
/* Detect if we need root rights, except when overriden by the config */
if (needs_root_rights == -1) {
for (i = 0; i < 16; i++) {
snprintf(buf, sizeof(buf), DRM_DEV_NAME, DRM_DIR_NAME, i);
fd = open(buf, O_RDWR);
if (fd == -1)
continue;
total_cards++;
memset(&res, 0, sizeof(struct drm_mode_card_res));
r = ioctl(fd, DRM_IOCTL_MODE_GETRESOURCES, &res);
if (r == 0 && res.count_connectors > 0)
kms_cards++;
close(fd);
}
}
/* If we've found cards, and all cards support kms, drop root rights */
if (needs_root_rights == 0 || (total_cards && kms_cards == total_cards)) {
gid_t realgid = getgid();
uid_t realuid = getuid();
if (setresgid(-1, realgid, realgid) != 0) {
perror("Could not drop setgid privileges");
exit(1);
}
if (setresuid(-1, realuid, realuid) != 0) {
perror("Could not drop setuid privileges");
exit(1);
}
}
snprintf(buf, sizeof(buf), "%s/Xorg.bin", SUID_WRAPPER_DIR);
/* Check if the server is executable by our real uid */
if (access(buf, X_OK) != 0) {
perror("Missing execute permissions for " SUID_WRAPPER_DIR "Xorg.bin");
exit(1);
}
argv[0] = buf;
(void) execv(argv[0], argv);
perror("Failed to execute " SUID_WRAPPER_DIR "/Xorg.bin");
exit(1);
}
......@@ -288,9 +288,15 @@
/* Support SHAPE extension */
#undef SHAPE
/* Where to install Xorg.bin and Xorg.wrap */
#undef SUID_WRAPPER_DIR
/* Define to 1 on systems derived from System V Release 4 */
#undef SVR4
/* sysconfdir */
#undef SYSCONFDIR
/* Support TCP socket connections */
#undef TCPCONN
......
......@@ -26,9 +26,6 @@
/* Vendor web address for support */
#undef __VENDORDWEBSUPPORT__
/* Location of system.XWinrc */
#undef SYSCONFDIR
/* Default log location */
#undef DEFAULT_LOGDIR
......
......@@ -31,6 +31,7 @@ MAN_SUBSTS += -e 's|__logdir__|$(logdir)|g' \
-e 's|__XKB_DFLT_OPTIONS__|$(XKB_DFLT_OPTIONS)|g' \
-e 's|__bundle_id_prefix__|$(BUNDLE_ID_PREFIX)|g' \
-e 's|__modulepath__|$(DEFAULT_MODULE_PATH)|g' \
-e 's|__suid_wrapper_dir__|$(SUID_WRAPPER_DIR)|g' \
-e 's|__default_font_path__|$(COMPILEDDEFAULTFONTPATH)|g' \
-e '\|$(COMPILEDDEFAULTFONTPATH)| s|/,|/, |g'
......
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