[Bug 1750013] [NEW] systemd-logind: memory leaks on session's connections (trusty-only)

[Guilherme G. Piccoli]

Public bug reported:

It was observed that systemd-logind tool is leaking memory at each session
connected. The issue happens in systemd from Trusty (14.04), which latest
version currently (Feb/2018) is 204-5ubuntu20.26 (and still reproduces
the bug).

The basic test-case is to run the following loop from a remote machine:

while true; do ssh <hostname-target> "whoami"; done

and watch the increase in memory consumption from "systemd-logind" process
in the target machine. One can use the "ps uax" command to verify the
RSS of the process, or count the anon pages from /proc/<logind_pid>/smaps.

To clarify a bit how a session works, the following "stack trace" details
a bit which function calls happen when a SSH connection is opened, from
Trusty's systemd-logind point of view:


main() <logind.c>
manager_startup()
manager_run() [event-loop]
bus_loop_dispatch() <dbus-loop.c>
dbus_watch_handle() -> bus_manager_message_handler()
bus_manager_create_session()
manager_add_session() <logind.c>
session_new() <logind-session.c>
session_create_fifo()
session_start()
session_create_cgroup()
session_save()
session_bus_path()
[...]

After each session is closed, it was observed that session_free() isn't
called, keeping the sessions alive. This can be verified through the
command "loginctl list-session" - each session that once connected is
present there "forever".

The memory leaks can eventually lead to OOM situation of this process.
Debug progress will be tracked here, in this LP.

** Affects: systemd (Ubuntu)
     Importance: Undecided
     Assignee: Guilherme G. Piccoli (gpiccoli)
         Status: New


** Tags: sts

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https://bugs.launchpad.net/bugs/1750013

Title:
  systemd-logind: memory leaks on session's connections (trusty-only)

Status in systemd package in Ubuntu:
  New

Bug description:
  It was observed that systemd-logind tool is leaking memory at each session
  connected. The issue happens in systemd from Trusty (14.04), which latest
  version currently (Feb/2018) is 204-5ubuntu20.26 (and still reproduces
  the bug).

  The basic test-case is to run the following loop from a remote
  machine:

  while true; do ssh <hostname-target> "whoami"; done

  and watch the increase in memory consumption from "systemd-logind" process
  in the target machine. One can use the "ps uax" command to verify the
  RSS of the process, or count the anon pages from /proc/<logind_pid>/smaps.

  To clarify a bit how a session works, the following "stack trace" details
  a bit which function calls happen when a SSH connection is opened, from
  Trusty's systemd-logind point of view:

  
  main() <logind.c>
  manager_startup()
  manager_run() [event-loop]
  bus_loop_dispatch() <dbus-loop.c>
  dbus_watch_handle() -> bus_manager_message_handler()
  bus_manager_create_session()
  manager_add_session() <logind.c>
  session_new() <logind-session.c>
  session_create_fifo()
  session_start()
  session_create_cgroup()
  session_save()
  session_bus_path()
  [...]

  After each session is closed, it was observed that session_free() isn't
  called, keeping the sessions alive. This can be verified through the
  command "loginctl list-session" - each session that once connected is
  present there "forever".

  The memory leaks can eventually lead to OOM situation of this process.
  Debug progress will be tracked here, in this LP.

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