From 7b377456f95d2ec3ead40f4fb74ea620191f88c8 Mon Sep 17 00:00:00 2001
From: Michal Srb <msrb@suse.com>
Date: Thu, 26 Oct 2017 09:48:13 +0200
Subject: Open files with O_NOFOLLOW. (CVE-2017-16611)

A non-privileged X client can instruct X server running under root to open any
file by creating own directory with "fonts.dir", "fonts.alias" or any font file
being a symbolic link to any other file in the system. X server will then open
it. This can be issue with special files such as /dev/watchdog.

Reviewed-by: Matthieu Herrb <matthieu@herrb.eu>
---
 src/fontfile/dirfile.c | 25 ++++++++++++++++++++++---
 src/fontfile/fileio.c  |  5 ++++-
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/src/fontfile/dirfile.c b/src/fontfile/dirfile.c
index 04cfa40..2802980 100644
--- a/src/fontfile/dirfile.c
+++ b/src/fontfile/dirfile.c
@@ -42,6 +42,7 @@ in this Software without prior written authorization from The Open Group.
 #include <stdio.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <fcntl.h>
 #include <errno.h>
 #include <limits.h>
 
@@ -61,8 +62,9 @@ FontFileReadDirectory (const char *directory, FontDirectoryPtr *pdir)
     char        dir_file[MAXFONTFILENAMELEN];
     char	dir_path[MAXFONTFILENAMELEN];
     char	*ptr;
-    FILE       *file;
-    int         count,
+    FILE       *file = 0;
+    int         file_fd,
+                count,
                 num_fonts,
                 status;
     struct stat	statb;
@@ -92,7 +94,14 @@ FontFileReadDirectory (const char *directory, FontDirectoryPtr *pdir)
     if (dir_file[strlen(dir_file) - 1] != '/')
 	strcat(dir_file, "/");
     strcat(dir_file, FontDirFile);
+#ifndef WIN32
+    file_fd = open(dir_file, O_RDONLY | O_NOFOLLOW);
+    if (file_fd >= 0) {
+	file = fdopen(file_fd, "rt");
+    }
+#else
     file = fopen(dir_file, "rt");
+#endif
     if (file) {
 #ifndef WIN32
 	if (fstat (fileno(file), &statb) == -1)
@@ -262,7 +271,8 @@ ReadFontAlias(char *directory, Bool isFile, FontDirectoryPtr *pdir)
     char		alias[MAXFONTNAMELEN];
     char		font_name[MAXFONTNAMELEN];
     char		alias_file[MAXFONTFILENAMELEN];
-    FILE		*file;
+    int			file_fd;
+    FILE		*file = 0;
     FontDirectoryPtr	dir;
     int			token;
     char		*lexToken;
@@ -280,7 +290,16 @@ ReadFontAlias(char *directory, Bool isFile, FontDirectoryPtr *pdir)
 	    strcat(alias_file, "/");
 	strcat(alias_file, FontAliasFile);
     }
+
+#ifndef WIN32
+    file_fd = open(alias_file, O_RDONLY | O_NOFOLLOW);
+    if (file_fd >= 0) {
+	file = fdopen(file_fd, "rt");
+    }
+#else
     file = fopen(alias_file, "rt");
+#endif
+
     if (!file)
 	return ((errno == ENOENT) ? Successful : BadFontPath);
     if (!dir)
diff --git a/src/fontfile/fileio.c b/src/fontfile/fileio.c
index 074ebcb..05374b4 100644
--- a/src/fontfile/fileio.c
+++ b/src/fontfile/fileio.c
@@ -40,6 +40,9 @@ in this Software without prior written authorization from The Open Group.
 #ifndef O_CLOEXEC
 #define O_CLOEXEC 0
 #endif
+#ifndef O_NOFOLLOW
+#define O_NOFOLLOW 0
+#endif
 
 FontFilePtr
 FontFileOpen (const char *name)
@@ -48,7 +51,7 @@ FontFileOpen (const char *name)
     int		len;
     BufFilePtr	raw, cooked;
 
-    fd = open (name, O_BINARY|O_CLOEXEC);
+    fd = open (name, O_BINARY|O_CLOEXEC|O_NOFOLLOW);
     if (fd < 0)
 	return 0;
     raw = BufFileOpenRead (fd);