Public bug reported:
[Impact]
Scope file leakage can cause SSH delays and reduce performance in systemd
[Description]
The current systemd-logind version present in Xenial can leave abandoned SSH
sessions and scope files in cases where the host sees a lot of concurrent SSH
connections. These leftover sessions can slow down systemd performance
greatly, and can have an impact on sshd handling a great number of concurrent
connections.
To fix this issue, patches are needed in both dbus and systemd. These improve
the
performance of the communication between dbus and systemd, so that they can
handle a better volume of events (e.g. SSH logins). All of those patches are
already present from Bionic onwards, so we only need those fixes for Xenial.
== Systemd ==
Upstream patches:
- core: use an AF_UNIX/SOCK_DGRAM socket for cgroup agent notification
(d8fdc62037b5)
- tree-wide: introduce new SOCKADDR_UN_LEN() macro, and use it everywhere
(fc2fffe7706e)
- journald: stack allocation cannot fail (23be5709e10b)
$ git describe --contains d8fdc62037b5 fc2fffe7706e 23be5709e10b
v230~71^2~2
v230~71^2~1
v230~71^2
$ rmadison systemd
systemd | 229-4ubuntu4 | xenial | source, ...
systemd | 229-4ubuntu21.21 | xenial-security | source, ...
systemd | 229-4ubuntu21.22 | xenial-updates | source, ... <--------
systemd | 237-3ubuntu10 | bionic | source, ...
systemd | 237-3ubuntu10.29 | bionic-security | source, ...
systemd | 237-3ubuntu10.29 | bionic-updates | source, ...
systemd | 237-3ubuntu10.31 | bionic-proposed | source, ...
== DBus ==
Upstream patches:
- Only read one message at a time if there are fds pending (892f084eeda0)
- bus: Fix timeout restarts (529600397bca)
- DBusMainLoop: ensure all required timeouts are restarted (446b0d9ac75a)
$ git describe --contains 892f084eeda0 529600397bca 446b0d9ac75a
dbus-1.11.10~44
dbus-1.11.10~45
dbus-1.11.16~2
$ rmadison dbus
dbus | 1.10.6-1ubuntu3 | xenial | source, ...
dbus | 1.10.6-1ubuntu3.4 | xenial-security | source, ...
dbus | 1.10.6-1ubuntu3.4 | xenial-updates | source, ... <--------
dbus | 1.12.2-1ubuntu1 | bionic | source, ...
dbus | 1.12.2-1ubuntu1.1 | bionic-security | source, ...
dbus | 1.12.2-1ubuntu1.1 | bionic-updates | source, ...
[Test Case]
1) Simulate a lot of concurrent SSH connections with e.g. a for loop:
multipass@xenial-logind:~$ for i in {1..1000}; do sleep 0.1; ssh localhost
sleep 1 > /dev/null & done
2) Check for leaked sessions in /run/systemd/system/:
multipass@xenial-logind:~$ ls -ld /run/systemd/system/session-*.scope*
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-103.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-104.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-105.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-106.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-110.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-111.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-112.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-113.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-114.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-115.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-116.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-117.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-118.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-119.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-120.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-121.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-122.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-123.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-126.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-131.scope.d
drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-134.scope.d
...
[Regression Potential]
The regression potential is low, as these patches have seen extensive testing
both upstream and in more recent releases of Ubuntu. Nonetheless, these new
packages will be rigorously tested through autopkgtest to avoid any possible
Xenial-specific regressions.
** Affects: dbus (Ubuntu)
Importance: Undecided
Status: Fix Released
** Affects: systemd (Ubuntu)
Importance: Undecided
Status: Fix Released
** Affects: dbus (Ubuntu Xenial)
Importance: Undecided
Assignee: Heitor Alves de Siqueira (halves)
Status: New
** Affects: systemd (Ubuntu Xenial)
Importance: Undecided
Assignee: Heitor Alves de Siqueira (halves)
Status: New
** Tags: sts
** Also affects: dbus (Ubuntu)
Importance: Undecided
Status: New
** Also affects: dbus (Ubuntu Xenial)
Importance: Undecided
Status: New
** Also affects: systemd (Ubuntu Xenial)
Importance: Undecided
Status: New
** Changed in: dbus (Ubuntu)
Status: New => Fix Released
** Changed in: systemd (Ubuntu)
Status: New => Fix Released
** Changed in: dbus (Ubuntu Xenial)
Assignee: (unassigned) => Heitor Alves de Siqueira (halves)
** Changed in: systemd (Ubuntu Xenial)
Assignee: (unassigned) => Heitor Alves de Siqueira (halves)
** Description changed:
[Impact]
Scope file leakage can cause SSH delays and reduce performance in systemd
[Description]
The current systemd-logind version present in Xenial can leave abandoned SSH
sessions and scope files in cases where the host sees a lot of concurrent SSH
connections. These leftover sessions can slow down systemd performance
greatly, and can have an impact on sshd handling a great number of concurrent
connections.
To fix this issue, patches are needed in both dbus and systemd. These improve
the
performance of the communication between dbus and systemd, so that they can
handle a better volume of events (e.g. SSH logins). All of those patches are
already present from Bionic onwards, so we only need those fixes for Xenial.
== Systemd ==
Upstream patches:
- core: use an AF_UNIX/SOCK_DGRAM socket for cgroup agent notification
(d8fdc62037b5)
- tree-wide: introduce new SOCKADDR_UN_LEN() macro, and use it everywhere
(fc2fffe7706e)
- journald: stack allocation cannot fail (23be5709e10b)
$ git describe --contains d8fdc62037b5 fc2fffe7706e 23be5709e10b
v230~71^2~2
v230~71^2~1
v230~71^2
$ rmadison systemd
- systemd | 229-4ubuntu4 | xenial | source, ...
- systemd | 229-4ubuntu21.21 | xenial-security | source, ...
- systemd | 229-4ubuntu21.22 | xenial-updates | source, ... <--------
- systemd | 237-3ubuntu10 | bionic | source, ...
- systemd | 237-3ubuntu10.29 | bionic-security | source, ...
- systemd | 237-3ubuntu10.29 | bionic-updates | source, ...
- systemd | 237-3ubuntu10.31 | bionic-proposed | source, ...
+ systemd | 229-4ubuntu4 | xenial | source, ...
+ systemd | 229-4ubuntu21.21 | xenial-security | source, ...
+ systemd | 229-4ubuntu21.22 | xenial-updates | source, ... <--------
+ systemd | 237-3ubuntu10 | bionic | source, ...
+ systemd | 237-3ubuntu10.29 | bionic-security | source, ...
+ systemd | 237-3ubuntu10.29 | bionic-updates | source, ...
+ systemd | 237-3ubuntu10.31 | bionic-proposed | source, ...
== DBus ==
Upstream patches:
- Only read one message at a time if there are fds pending (892f084eeda0)
- bus: Fix timeout restarts (529600397bca)
- DBusMainLoop: ensure all required timeouts are restarted (446b0d9ac75a)
$ git describe --contains 892f084eeda0 529600397bca 446b0d9ac75a
dbus-1.11.10~44
dbus-1.11.10~45
dbus-1.11.16~2
$ rmadison dbus
- dbus | 1.10.6-1ubuntu3 | xenial | source, ...
- dbus | 1.10.6-1ubuntu3.4 | xenial-security | source, ...
- dbus | 1.10.6-1ubuntu3.4 | xenial-updates | source, ... <--------
- dbus | 1.12.2-1ubuntu1 | bionic | source, ...
- dbus | 1.12.2-1ubuntu1.1 | bionic-security | source, ...
- dbus | 1.12.2-1ubuntu1.1 | bionic-updates | source, ...
+ dbus | 1.10.6-1ubuntu3 | xenial | source, ...
+ dbus | 1.10.6-1ubuntu3.4 | xenial-security | source, ...
+ dbus | 1.10.6-1ubuntu3.4 | xenial-updates | source, ... <--------
+ dbus | 1.12.2-1ubuntu1 | bionic | source, ...
+ dbus | 1.12.2-1ubuntu1.1 | bionic-security | source, ...
+ dbus | 1.12.2-1ubuntu1.1 | bionic-updates | source, ...
[Test Case]
1) Simulate a lot of concurrent SSH connections with e.g. a for loop:
multipass@xenial-logind:~$ for i in {1..1000}; do sleep 0.1; ssh localhost
sleep 1 > /dev/null & done
2) Check for leaked sessions in /run/systemd/system/:
multipass@xenial-logind:~$ ls -ld /run/systemd/system/session-*.scope*
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-103.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-104.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-105.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-106.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-110.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-111.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-112.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-113.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-114.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-115.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-116.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-117.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-118.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-119.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-120.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-121.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-122.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-123.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-126.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-131.scope.d
- drwxr-xr-x 2 root root 160 Oct 4 15:34
/run/systemd/system/session-134.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-103.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-104.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-105.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-106.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-110.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-111.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-112.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-113.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-114.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-115.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-116.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-117.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-118.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-119.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-120.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-121.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-122.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-123.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-126.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-131.scope.d
+ drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-134.scope.d
...
[Regression Potential]
The regression potential is low, as these patches have seen extensive testing
both upstream and in more recent releases of Ubuntu. Nonetheless, these new
packages will be rigorously tested through autopkgtest to avoid any possible
Xenial-specific regressions.
--
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https://bugs.launchpad.net/bugs/1846787
Title:
systemd-logind leaves leftover sessions and scope files
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