[systemd-devel] [Patch 0/2] logind: make sure that closed sessions will be cleaned

[Djalal Harouni]

ping?

(Please if I'm missing something let me know)

On Fri, Jan 03, 2014 at 02:19:19PM +0100, Djalal Harouni wrote:
> On logout pam_systemd should ensures the following:
> "If the last concurrent session of a user ends, the $XDG_RUNTIME_DIR
> directory and all its contents are removed, too." from manpage.
> 
> Using git HEAD, and a simple systemd-nspawn test will show that the
> above is not ensured and the sessions will stay!
> 
> 
> A simple systemd-nspawn test:
> 
> 1) login as user X
> 2) logout
> 3) login as user Y
> 4) loginctl      (will list session of user X)
> 
> 
> In this example we are session c4:
> 
> -bash-4.2# loginctl list-sessions
>    SESSION        UID USER             SEAT 
>          1       1000 tixxdz           seat0 
>         c1       1000 tixxdz           seat0
>         c2          0 root             seat0
>         c3       1000 tixxdz           seat0
>         c4          0 root             seat0
> 
> -bash-4.2# loginctl show-session --property=State 1 c1 c2 c3 c4
> State=closing
> 
> State=closing
> 
> State=closing
> 
> State=closing
> 
> State=active
> 
> 
> As shown only session c4 is active, all the others are dead sessions.
> 
> To close the dead sessions and clean things up, a dbus
> TerminateSession()=>session_stop() must be issued...
> 
> Please note that I'm running without pam_loginuid.so, due to another
> bug related to audit: https://bugzilla.redhat.com/show_bug.cgi?id=966807
> 
> 
> Anyway, after some debugging:
> 
> It seems that after ReleaseSession() which is called by pam_systemd,
> the user,session and seat state files will also still be available.
> The garbage-collector will miss them!
> 
> In src/login/logind.c:manager_gc() the while loops will never be entered.
> 
> 
> The user slice units will start, then the match_job_removed() and co
> signals on these units will call session_add_to_gc_queue() and
> user_add_to_gc_queue() to push to gc_queue when done, in the mean time
> the manager_gc() will consume the gc_queue and remove them
> 
> IOW *just* before and after the ReleaseSession() the manager
> "{session|user}_gc_queue" queues might be empty, hence session, users
> and seats will never be cleaned! the user's slice will still be alive...
> 
> 
> To fix this, I'm attaching two patches and I can say that they are
> related to each other from the perspective of the described bug, and at
> the same time they are independent of each other from a general
> perspective!
> 
> 
> 1) Make method_release_session() call session_add_to_gc_queue()
> This will ensure that the released session is in the gc_queue.
> 
> This change gives the garbage collector a chance to collect sessions,
> and should not affect the logind behaviour and other display managers,
> the session_check_gc() is able to detect if the session is still valid.
> 
> The thing is that from a quick git log the method_release_session()
> never called session_add_to_gc_queue(), so this bug was introduced or
> made *visible* by another change... (not sure)
> 
> 
> 2) As in commit 63966da86d8e, in function session_check_gc() the session
> manager will always be around so don't check it in order to
> garbage-collect the session.
> 
> Thanks!
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> systemd-devel at lists.freedesktop.org
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-- 
Djalal Harouni
http://opendz.org