ddxLoad: Check XDG_RUNTIME_DIR before fallback to /tmp/

The XKM_OUTPUT_DIR folder by default is defined as ${datadir}/X11/xkb/compiled
and it is usually defined as /var/lib/xkb or %{_localstatedir}/lib/xkb by
distributions. If X is executed as non-root it won't have permissions to write
into that folder. If we fallback directly to /tmp we might get name collisions:
```
> Error: Cannot open "/tmp/server-10.xkm" to write keyboard description
> Exiting
```

Where the file /tmp/server-10.xkm already exists but is owned by another user
that previously executed X and had the display number 10. This is specially
problematic when exeuting Xvfb.

Before falling back to /tmp/ check first the XDG_RUNTIME_DIR.

1 files changed, 11 insertions, 2 deletions

diff --git a/xkb/ddxLoad.c b/xkb/ddxLoad.c
index 2d203ce11..18814264a 100644
--- a/xkb/ddxLoad.c
+++ b/xkb/ddxLoad.c
@@ -31,6 +31,7 @@ THE USE OR PERFORMANCE OF THIS SOFTWARE.
 #include <xkb-config.h>
 
 #include <stdio.h>
+#include <stdlib.h>
 #include <ctype.h>
 #include <X11/X.h>
 #include <X11/Xos.h>
@@ -69,9 +70,17 @@ OutputDirectory(char *outdir, size_t size)
     /* Can we write an xkm and then open it too? */
     if (access(XKM_OUTPUT_DIR, W_OK | X_OK) == 0) {
         directory = XKM_OUTPUT_DIR;
-        if (XKM_OUTPUT_DIR[strlen(XKM_OUTPUT_DIR) - 1] != '/')
-            pathsep = "/";
+    } else {
+        const char *xdg_runtime_dir = getenv("XDG_RUNTIME_DIR");
+
+        if (xdg_runtime_dir && xdg_runtime_dir[0] == '/' &&
+            access(xdg_runtime_dir, W_OK | X_OK) == 0)
+            directory = xdg_runtime_dir;
     }
+
+    if (directory && directory[strlen(directory) - 1] != '/')
+        pathsep = "/";
+
 #else
     directory = Win32TempDir();
     pathsep = "\\";