[pulseaudio-discuss] [PATCH v2] core-util: Fail if XDG_RUNTIME_DIR belongs to someone else

[David Henningsson]

Usually, PA will use the PULSE_SERVER X11 property instead of using XDG_RUNTIME_DIR,
so this environment variable does not matter.

If this property is not available, or if one is using the pacmd cli protocol,
the client will go ahead and call pa_make_secure_dir on XDG_RUNTIME_DIR/pulse.
This will either fail (if you're another regular user), or succeed (if you're root).
Both scenarios are bad - failing will cause the connection to fail, and succeeding
is even worse, as it can cause *other* connections to fail (as the directory
ownership has changed).

Instead fail and complain loudly.

BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=83007
Signed-off-by: David Henningsson <david.henningsson at canonical.com>
---
 src/pulsecore/core-util.c | 8 ++++++++
 1 file changed, 8 insertions(+)

v2: Don't blame systemd anymore. Make error message translatable.

diff --git a/src/pulsecore/core-util.c b/src/pulsecore/core-util.c
index d7a95d6..6bb6317 100644
--- a/src/pulsecore/core-util.c
+++ b/src/pulsecore/core-util.c
@@ -1816,6 +1816,14 @@ char *pa_get_runtime_dir(void) {
     /* Use the XDG standard for the runtime directory. */
     d = getenv("XDG_RUNTIME_DIR");
     if (d) {
+        struct stat st;
+        if (stat(d, &st) == 0 && st.st_uid != getuid()) {
+            pa_log(_("XDG_RUNTIME_DIR (%s) is not owned by us (uid %d), but by uid %d!\n"
+                   "(This could e g happen if you try to connect to a non-root PulseAudio as a root user, over the native protocol. Don't do that.)"),
+                   d, getuid(), st.st_uid);
+            goto fail;
+        }
+
         k = pa_sprintf_malloc("%s" PA_PATH_SEP "pulse", d);
 
         if (pa_make_secure_dir(k, m, (uid_t) -1, (gid_t) -1, true) < 0) {
-- 
1.9.1