Incorrect command-line parameter validation in the Xorg X server can lead to
privilege elevation and/or arbitrary files overwrite, when the X server is
running with elevated privileges (ie when Xorg is installed with the setuid bit
set and started by a non-root user). The -modulepath argument can be used to
specify an insecure path to modules that are going to be loaded in the X server,
allowing to execute unprivileged code in the privileged process. The -logfile
argument can be used to overwrite arbitrary files in the file system, due to
incorrect checks in the parsing of the option.

CVE: CVE-2018-14665
Upstream-Status: Backport
Signed-off-by: Ross Burton <ross.burton@intel.com>

From 50c0cf885a6e91c0ea71fb49fa8f1b7c86fe330e Mon Sep 17 00:00:00 2001
From: Matthieu Herrb <matthieu@herrb.eu>
Date: Tue, 23 Oct 2018 21:29:08 +0200
Subject: [PATCH] Disable -logfile and -modulepath when running with elevated
 privileges

Could cause privilege elevation and/or arbitrary files overwrite, when
the X server is running with elevated privileges (ie when Xorg is
installed with the setuid bit set and started by a non-root user).

CVE-2018-14665

Issue reported by Narendra Shinde and Red Hat.

Signed-off-by: Matthieu Herrb <matthieu@herrb.eu>
Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Adam Jackson <ajax@redhat.com>
---
 hw/xfree86/common/xf86Init.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/hw/xfree86/common/xf86Init.c b/hw/xfree86/common/xf86Init.c
index 6c25eda73..0f57efa86 100644
--- a/hw/xfree86/common/xf86Init.c
+++ b/hw/xfree86/common/xf86Init.c
@@ -935,14 +935,18 @@ ddxProcessArgument(int argc, char **argv, int i)
     /* First the options that are not allowed with elevated privileges */
     if (!strcmp(argv[i], "-modulepath")) {
         CHECK_FOR_REQUIRED_ARGUMENT();
-        xf86CheckPrivs(argv[i], argv[i + 1]);
+        if (xf86PrivsElevated())
+              FatalError("\nInvalid argument -modulepath "
+                "with elevated privileges\n");
         xf86ModulePath = argv[i + 1];
         xf86ModPathFrom = X_CMDLINE;
         return 2;
     }
     if (!strcmp(argv[i], "-logfile")) {
         CHECK_FOR_REQUIRED_ARGUMENT();
-        xf86CheckPrivs(argv[i], argv[i + 1]);
+        if (xf86PrivsElevated())
+              FatalError("\nInvalid argument -logfile "
+                "with elevated privileges\n");
         xf86LogFile = argv[i + 1];
         xf86LogFileFrom = X_CMDLINE;
         return 2;
-- 
2.18.1