Bug#817998: /lib/x86_64-linux-gnu/libsystemd.so.0: sd_pid_get_session incorrectly(?) returning -ENXIO (sesion does not exist)

[Sam Morris]

Package: libsystemd0
Version: 229-2
Severity: normal
File: /lib/x86_64-linux-gnu/libsystemd.so.0

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I'm trying to work out why I get the following:

	/usr/lib/policykit-1-gnome/polkit-gnome-authentication-agent-1

	(polkit-gnome-authentication-agent-1:14272): polkit-gnome-1-WARNING **: Unable to determine the session we are in: No session for pid 14272

This calls sd_pid_get_session on its own pid, which returns -ENXIO. But... I have a
session, haven't I?

	$ loginctl show-session $XDG_SESSION_ID
	Id=1
	User=1000
	Name=sam
	Timestamp=Sat 2016-03-12 09:42:18 GMT
	TimestampMonotonic=67859194
	VTNr=2
	Seat=seat0
	TTY=/dev/tty2
	Remote=no
	Service=gdm-password
	Scope=session-1.scope
	Leader=1785
	Audit=1
	Type=x11
	Class=user
	Active=yes
	State=active
	IdleHint=yes
	IdleSinceHint=1457700819192000
	IdleSinceHintMonotonic=0

Internally, sd_pid_get_session calls cg_pid_get_session on that pid,
which calls cg_pid_get_path_shifted, which returns
"/user.slice/user-1000.slice/user at 1000.service/dbus.service". This path
is then passed to cg_path_get_session, which calls cg_path_get_unit on
it, resulting in "user at 1000.service". cg_path_get_session then bails
because this string does not start with "session-".

At this point I don't know whether polkit is using the API incorrectly,
or whether there is a genuine problem with libsystemd. But the result of
cg_pid_get_path_shifted looks strange... the code expects it to look
more like "/user.slice/user-1000.slice/session-1.scope".

- -- System Information:
Debian Release: 8.3
  APT prefers stable-updates
  APT policy: (550, 'stable-updates'), (550, 'stable'), (530, 'testing'), (520, 'unstable'), (510, 'experimental'), (500, 'unstable-debug'), (500, 'testing-updates')
Architecture: amd64 (x86_64)

Kernel: Linux 4.4.0-1-amd64 (SMP w/2 CPU cores)
Locale: LANG=en_GB.utf8, LC_CTYPE=en_GB.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages libsystemd0:amd64 depends on:
ii  libc6        2.21-9
ii  libgcrypt20  1.6.3-2+deb8u1
ii  liblzma5     5.1.1alpha+20120614-2+b3
ii  libselinux1  2.3-2

libsystemd0:amd64 recommends no packages.

libsystemd0:amd64 suggests no packages.

- -- no debconf information

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