[PATCH xserver] xserver: check for elevated privileges not uid=0
Antoine Martin
antoine at nagafix.co.uk
Fri Dec 16 10:36:51 PST 2011
This allows us to run the server as a normal user whilst still
being able to use the -modulepath, -logfile and -config switches
We define a xf86PrivsElevated which will do the checks and cache
the result in case it is called more than once.
Also renamed the paths #defines to match their new meaning.
Original discussion which led to this patch can be found here:
http://lists.freedesktop.org/archives/xorg-devel/2011-September/025853.html
Signed-off-by: Antoine Martin <antoine at nagafix.co.uk>
Tested-by: Michal Suchanek <hramrach at centrum.cz>
Reviewed-by: Jamey Sharp <jamey at minilop.net>
Reviewed-by: Adam Jackson <ajax at redhat.com>
---
configure.ac | 2 +-
hw/xfree86/common/xf86Config.c | 28 +++++++-------
hw/xfree86/common/xf86Init.c | 78 +++++++++++++++++++++++++++++++++++-----
hw/xfree86/common/xf86Priv.h | 1 +
include/xorg-config.h.in | 6 +++
5 files changed, 91 insertions(+), 24 deletions(-)
diff --git a/configure.ac b/configure.ac
index 27bf6ab..518eb06 100644
--- a/configure.ac
+++ b/configure.ac
@@ -212,7 +212,7 @@ AC_CHECK_FUNC([dlopen], [],
AC_SUBST(DLOPEN_LIBS)
dnl Checks for library functions.
-AC_CHECK_FUNCS([backtrace ffs \
+AC_CHECK_FUNCS([backtrace ffs geteuid getuid issetugid getresuid \
getdtablesize getifaddrs getpeereid getpeerucred getzoneid \
mmap shmctl64 strncasecmp vasprintf vsnprintf walkcontext])
AC_REPLACE_FUNCS([strcasecmp strcasestr strlcat strlcpy strndup])
diff --git a/hw/xfree86/common/xf86Config.c b/hw/xfree86/common/xf86Config.c
index 569695c..f51be7e 100644
--- a/hw/xfree86/common/xf86Config.c
+++ b/hw/xfree86/common/xf86Config.c
@@ -72,8 +72,8 @@
* These paths define the way the config file search is done. The escape
* sequences are documented in parser/scan.c.
*/
-#ifndef ROOT_CONFIGPATH
-#define ROOT_CONFIGPATH "%A," "%R," \
+#ifndef ALL_CONFIGPATH
+#define ALL_CONFIGPATH "%A," "%R," \
"/etc/X11/%R," "%P/etc/X11/%R," \
"%E," "%F," \
"/etc/X11/%F," "%P/etc/X11/%F," \
@@ -83,8 +83,8 @@
"%P/lib/X11/%X.%H," \
"%P/lib/X11/%X"
#endif
-#ifndef USER_CONFIGPATH
-#define USER_CONFIGPATH "/etc/X11/%S," "%P/etc/X11/%S," \
+#ifndef RESTRICTED_CONFIGPATH
+#define RESTRICTED_CONFIGPATH "/etc/X11/%S," "%P/etc/X11/%S," \
"/etc/X11/%G," "%P/etc/X11/%G," \
"/etc/X11/%X," "/etc/%X," \
"%P/etc/X11/%X.%H," \
@@ -92,14 +92,14 @@
"%P/lib/X11/%X.%H," \
"%P/lib/X11/%X"
#endif
-#ifndef ROOT_CONFIGDIRPATH
-#define ROOT_CONFIGDIRPATH "%A," "%R," \
+#ifndef ALL_CONFIGDIRPATH
+#define ALL_CONFIGDIRPATH "%A," "%R," \
"/etc/X11/%R," "%C/X11/%R," \
"/etc/X11/%X," "%C/X11/%X"
#endif
-#ifndef USER_CONFIGDIRPATH
-#define USER_CONFIGDIRPATH "/etc/X11/%R," "%C/X11/%R," \
- "/etc/X11/%X," "%C/X11/%X"
+#ifndef RESTRICTED_CONFIGDIRPATH
+#define RESTRICTED_CONFIGDIRPATH "/etc/X11/%R," "%C/X11/%R," \
+ "/etc/X11/%X," "%C/X11/%X"
#endif
#ifndef SYS_CONFIGDIRPATH
#define SYS_CONFIGDIRPATH "/usr/share/X11/%X," "%D/X11/%X"
@@ -2310,12 +2310,12 @@ xf86HandleConfigFile(Bool autoconfig)
MessageType filefrom = X_DEFAULT;
MessageType dirfrom = X_DEFAULT;
- if (getuid() == 0) {
- filesearch = ROOT_CONFIGPATH;
- dirsearch = ROOT_CONFIGDIRPATH;
+ if (!xf86PrivsElevated()) {
+ filesearch = ALL_CONFIGPATH;
+ dirsearch = ALL_CONFIGDIRPATH;
} else {
- filesearch = USER_CONFIGPATH;
- dirsearch = USER_CONFIGDIRPATH;
+ filesearch = RESTRICTED_CONFIGPATH;
+ dirsearch = RESTRICTED_CONFIGDIRPATH;
}
if (xf86ConfigFile)
diff --git a/hw/xfree86/common/xf86Init.c b/hw/xfree86/common/xf86Init.c
index c1e48ee..5263b5f 100644
--- a/hw/xfree86/common/xf86Init.c
+++ b/hw/xfree86/common/xf86Init.c
@@ -238,6 +238,65 @@ xf86PrintMarkers(void)
LogPrintMarkers();
}
+Bool xf86PrivsElevated(void)
+{
+ static Bool privsTested = FALSE;
+ static Bool privsElevated = TRUE;
+
+ if (!privsTested) {
+#if defined(WIN32)
+ privsElevated = FALSE;
+#else
+ if ((getuid() != geteuid()) || (getgid() != getegid())) {
+ privsElevated = TRUE;
+ } else {
+#if defined(HAVE_ISSETUGID)
+ privsElevated = issetugid();
+#elif defined(HAVE_GETRESUID)
+ uid_t ruid, euid, suid;
+ gid_t rgid, egid, sgid;
+
+ if ((getresuid(&ruid, &euid, &suid) == 0) &&
+ (getresgid(&rgid, &egid, &sgid) == 0)) {
+ privsElevated = (euid != suid) || (egid != sgid);
+ }
+ else {
+ printf("Failed getresuid or getresgid");
+ /* Something went wrong, make defensive assumption */
+ privsElevated = TRUE;
+ }
+#else
+ if (getuid()==0) {
+ /* running as root: uid==euid==0 */
+ privsElevated = FALSE;
+ }
+ else {
+ /*
+ * If there are saved ID's the process might still be privileged
+ * even though the above test succeeded. If issetugid() and
+ * getresgid() aren't available, test this by trying to set
+ * euid to 0.
+ */
+ unsigned int oldeuid;
+ oldeuid = geteuid();
+
+ if (seteuid(0) != 0) {
+ privsElevated = FALSE;
+ } else {
+ if (seteuid(oldeuid) != 0) {
+ FatalError("Failed to drop privileges. Exiting\n");
+ }
+ privsElevated = TRUE;
+ }
+ }
+#endif
+ }
+#endif
+ privsTested = TRUE;
+ }
+ return privsElevated;
+}
+
static Bool
xf86CreateRootWindow(WindowPtr pWin)
{
@@ -872,7 +931,7 @@ OsVendorInit(void)
#ifdef O_NONBLOCK
if (!beenHere) {
- if (geteuid() == 0 && getuid() != geteuid())
+ if (xf86PrivsElevated())
{
int status;
@@ -1043,10 +1102,11 @@ ddxProcessArgument(int argc, char **argv, int i)
FatalError("Required argument to %s not specified\n", argv[i]); \
}
- /* First the options that are only allowed for root */
+ /* First the options that are not allowed with elevated privileges */
if (!strcmp(argv[i], "-modulepath") || !strcmp(argv[i], "-logfile")) {
- if ( (geteuid() == 0) && (getuid() != 0) ) {
- FatalError("The '%s' option can only be used by root.\n", argv[i]);
+ if (xf86PrivsElevated()) {
+ FatalError("The '%s' option cannot be used with "
+ "elevated privileges.\n", argv[i]);
}
else if (!strcmp(argv[i], "-modulepath"))
{
@@ -1074,9 +1134,9 @@ ddxProcessArgument(int argc, char **argv, int i)
if (!strcmp(argv[i], "-config") || !strcmp(argv[i], "-xf86config"))
{
CHECK_FOR_REQUIRED_ARGUMENT();
- if (getuid() != 0 && !xf86PathIsSafe(argv[i + 1])) {
+ if (xf86PrivsElevated() && !xf86PathIsSafe(argv[i + 1])) {
FatalError("\nInvalid argument for %s\n"
- "\tFor non-root users, the file specified with %s must be\n"
+ "\tWith elevated privileges, the file specified with %s must be\n"
"\ta relative path and must not contain any \"..\" elements.\n"
"\tUsing default "__XCONFIGFILE__" search path.\n\n",
argv[i], argv[i]);
@@ -1087,9 +1147,9 @@ ddxProcessArgument(int argc, char **argv, int i)
if (!strcmp(argv[i], "-configdir"))
{
CHECK_FOR_REQUIRED_ARGUMENT();
- if (getuid() != 0 && !xf86PathIsSafe(argv[i + 1])) {
+ if (xf86PrivsElevated() && !xf86PathIsSafe(argv[i + 1])) {
FatalError("\nInvalid argument for %s\n"
- "\tFor non-root users, the file specified with %s must be\n"
+ "\tWith elevated privileges, the file specified with %s must be\n"
"\ta relative path and must not contain any \"..\" elements.\n"
"\tUsing default "__XCONFIGDIR__" search path.\n\n",
argv[i], argv[i]);
@@ -1375,7 +1435,7 @@ ddxUseMsg(void)
ErrorF("\n");
ErrorF("\n");
ErrorF("Device Dependent Usage\n");
- if (getuid() == 0 || geteuid() != 0)
+ if (!xf86PrivsElevated())
{
ErrorF("-modulepath paths specify the module search path\n");
ErrorF("-logfile file specify a log file name\n");
diff --git a/hw/xfree86/common/xf86Priv.h b/hw/xfree86/common/xf86Priv.h
index e0b1809..255407b 100644
--- a/hw/xfree86/common/xf86Priv.h
+++ b/hw/xfree86/common/xf86Priv.h
@@ -145,6 +145,7 @@ extern _X_EXPORT Bool xf86LoadModules(char **list, pointer *optlist);
extern _X_EXPORT int xf86SetVerbosity(int verb);
extern _X_EXPORT int xf86SetLogVerbosity(int verb);
extern _X_EXPORT Bool xf86CallDriverProbe( struct _DriverRec * drv, Bool detect_only );
+extern _X_EXPORT Bool xf86PrivsElevated(void);
#endif /* _NO_XF86_PROTOTYPES */
diff --git a/include/xorg-config.h.in b/include/xorg-config.h.in
index 6b9230f..2cc416a 100644
--- a/include/xorg-config.h.in
+++ b/include/xorg-config.h.in
@@ -130,4 +130,10 @@
/* Use libpciaccess */
#undef XSERVER_LIBPCIACCESS
+/* Have setugid */
+#undef HAVE_ISSETUGID
+
+/* Have getresuid */
+#undef HAVE_GETRESUID
+
#endif /* _XORG_CONFIG_H_ */
--
1.7.7.4
--------------000707000001090405060401--
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