Unexpected gdbus behaviour during PAM authentication

[Linus Lewandowski]

If you won't find a solution, you might want to try pam_exec.

On Sun, Jan 15, 2017, 02:27 David Llewellyn-Jones <david at flypig.co.uk>
wrote:

> On 13/01/17 15:47, Bastien Nocera wrote:
> > On Fri, 2017-01-13 at 14:37 +0000, David Llewellyn-Jones wrote:
> >>
> >> I've been experiencing strange behaviour connecting to the system bus
> >> from a pam module. This is on Ubuntu 16.04 using gdbus and gdbus-
> >> codegen
> >> for both the caller and listening service.
> >>
>
> [snip - gdbus details]
>
> >> Does anyone have any suggestion for why this might be happening?
> >
> > GDBus's threads and PAM really don't mix. You'll need to either use
> > something like dbus-glib, which is single-threaded and sync, move your
> > D-Bus code to a small helper you'd talk to over Unix sockets (yeah, I
> > know...), or wait until PAM dies.
> >
> > FWIW, this problem is one of the reasons why fprintd (and pam_fprintd)
> > is written using dbus-glib rather than GDBus.
>
> I've attempted to convert the pam module to use dbus-glib, using your
> pam_fprintd.c code as a template (which has been very helpful, thank
> you!). Unfortunately I'm still running in to problems.
>
> After removing all of the previous gdbus code and replacing it with the
> following dbus-glib code, I now get segfaults occurring.
>
> -------
> GError * error = NULL;
> DBusGConnection * connection;
>
> connection = dbus_g_bus_get (DBUS_BUS_SYSTEM, &error);
> if (connection == NULL) {
>   syslog(LOG_ERR, "pam_test: connection error: %s\n", error->message);
>   g_clear_error (&error);
> }
> else {
>   dbus_g_connection_unref (connection);
> }
> -------
>
> Originally I had a more complete set of code following this, but I found
> the above was enough to trigger the problem.
>
> Here's the code on github:
>
> https://github.com/llewelld/dbus-pam-test/blob/5940e11d939f587a7c1b42c00a02d0a5cc7dc2c3/src/pam_test.c#L131
>
> and here's the segfault entry from syslog:
>
> Jan 14 23:12:17 Owen kernel: [ 4683.886530] compiz[11249]: segfault at
> 7f34cd0ac8a0 ip 00007f34f8692908 sp 00007ffe6e955970 error 4 in
> libglib-2.0.so.0.4800.1[7f34f8649000+10f000]
>
> Am I doing something wrong? In case it's important, the segfault doesn't
> occur the first time the module is run, but consistently when it's
> called for a second time. Again, this is all using the Unity lockscreen
> on Ubuntu 16.04.
>
> David
> --
> Website: http://www.flypig.co.uk
> _______________________________________________
> dbus mailing list
> dbus at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dbus
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/dbus/attachments/20170115/ad7c110f/attachment.html>