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pid1: add D-Bus API for removing delegated subcgroups

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When running unprivileged containers, we run into a scenario where an
unpriv owned cgroup has a subcgroup delegated to another user (i.e. the
container's own UIDs). When the owner of that cgroup dies without
cleaning it up then the unpriv service manager might encounter a cgroup
it cannot delete anymore.

Let's address that: let's expose a method call on the service manager
(primarly in PID1) that can be used to delete a subcgroup of a unit one
owns. This would then allow the unpriv service manager to ask the priv
service manager to get rid of such a cgroup.

This commit only adds the method call, the next commit then adds the
code that makes use of this.
This commit is contained in:
Lennart Poettering
2025-01-08 15:27:25 +01:00
parent 59857b672c
commit 94634b4b03
7 changed files with 182 additions and 4 deletions
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man/org.freedesktop.systemd1.xml
+55 -4
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@@ -147,6 +147,9 @@ node /org/freedesktop/systemd1 {
AttachProcessesToUnit(in s unit_name,
in s subcgroup,
in au pids);
RemoveSubgroupFromUnit(in s unit_name,
in s subcgroup,
in t flags);
AbandonScope(in s name);
GetJob(in u id,
out o job);
@@ -870,6 +873,8 @@ node /org/freedesktop/systemd1 {
<variablelist class="dbus-method" generated="True" extra-ref="AttachProcessesToUnit()"/>
<variablelist class="dbus-method" generated="True" extra-ref="RemoveSubgroupFromUnit()"/>
<variablelist class="dbus-method" generated="True" extra-ref="AbandonScope()"/>
<variablelist class="dbus-method" generated="True" extra-ref="GetJob()"/>
@@ -1599,6 +1604,13 @@ node /org/freedesktop/systemd1 {
parameters. The possible values are <literal>configuration</literal>, <literal>state</literal>,
<literal>logs</literal>, <literal>cache</literal>, <literal>runtime</literal>,
<literal>fdstore</literal>, and <literal>all</literal>.</para>
<para><function>RemoveSubgroupFromUnit()</function> removes a subcgroup belonging to a unit's
cgroup. Takes three arguments: the unit name (if empty defaults to the caller's unit), a cgroup path
(which must start start with a slash <literal>/</literal>), which is taken relative to the unit's
cgroup, and a flags argument (which must be zero for now). This is primarily useful for unprivileged
service managers to ask the system service manager for removal of subcgroups it manages, in case one
was delegated to other UIDs.</para>
</refsect2>
<refsect2>
@@ -2704,6 +2716,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2eservice {
GetProcesses(out a(sus) processes);
AttachProcesses(in s subcgroup,
in au pids);
RemoveSubgroup(in s subcgroup,
in t flags);
properties:
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly s Type = '...';
@@ -3398,6 +3412,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2eservice {
<!--method AttachProcesses is not documented!-->
<!--method RemoveSubgroup is not documented!-->
<!--property Type is not documented!-->
<!--property ExitType is not documented!-->
@@ -4006,6 +4022,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2eservice {
<variablelist class="dbus-method" generated="True" extra-ref="AttachProcesses()"/>
<variablelist class="dbus-method" generated="True" extra-ref="RemoveSubgroup()"/>
<variablelist class="dbus-property" generated="True" extra-ref="Type"/>
<variablelist class="dbus-property" generated="True" extra-ref="ExitType"/>
@@ -4901,6 +4919,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2esocket {
GetProcesses(out a(sus) processes);
AttachProcesses(in s subcgroup,
in au pids);
RemoveSubgroup(in s subcgroup,
in t flags);
properties:
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly s BindIPv6Only = '...';
@@ -5592,6 +5612,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2esocket {
<!--method AttachProcesses is not documented!-->
<!--method RemoveSubgroup is not documented!-->
<!--property BindIPv6Only is not documented!-->
<!--property Backlog is not documented!-->
@@ -6206,6 +6228,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2esocket {
<variablelist class="dbus-method" generated="True" extra-ref="AttachProcesses()"/>
<variablelist class="dbus-method" generated="True" extra-ref="RemoveSubgroup()"/>
<variablelist class="dbus-property" generated="True" extra-ref="BindIPv6Only"/>
<variablelist class="dbus-property" generated="True" extra-ref="Backlog"/>
@@ -7001,6 +7025,8 @@ node /org/freedesktop/systemd1/unit/home_2emount {
GetProcesses(out a(sus) processes);
AttachProcesses(in s subcgroup,
in au pids);
RemoveSubgroup(in s subcgroup,
in t flags);
properties:
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly s Where = '...';
@@ -7601,6 +7627,8 @@ node /org/freedesktop/systemd1/unit/home_2emount {
<!--method AttachProcesses is not documented!-->
<!--method RemoveSubgroup is not documented!-->
<!--property Where is not documented!-->
<!--property What is not documented!-->
@@ -8141,6 +8169,8 @@ node /org/freedesktop/systemd1/unit/home_2emount {
<variablelist class="dbus-method" generated="True" extra-ref="AttachProcesses()"/>
<variablelist class="dbus-method" generated="True" extra-ref="RemoveSubgroup()"/>
<variablelist class="dbus-property" generated="True" extra-ref="Where"/>
<variablelist class="dbus-property" generated="True" extra-ref="What"/>
@@ -8991,6 +9021,8 @@ node /org/freedesktop/systemd1/unit/dev_2dsda3_2eswap {
GetProcesses(out a(sus) processes);
AttachProcesses(in s subcgroup,
in au pids);
RemoveSubgroup(in s subcgroup,
in t flags);
properties:
readonly s What = '...';
readonly i Priority = ...;
@@ -9577,6 +9609,8 @@ node /org/freedesktop/systemd1/unit/dev_2dsda3_2eswap {
<!--method AttachProcesses is not documented!-->
<!--method RemoveSubgroup is not documented!-->
<!--property What is not documented!-->
<!--property Priority is not documented!-->
@@ -10103,6 +10137,8 @@ node /org/freedesktop/systemd1/unit/dev_2dsda3_2eswap {
<variablelist class="dbus-method" generated="True" extra-ref="AttachProcesses()"/>
<variablelist class="dbus-method" generated="True" extra-ref="RemoveSubgroup()"/>
<variablelist class="dbus-property" generated="True" extra-ref="What"/>
<variablelist class="dbus-property" generated="True" extra-ref="Priority"/>
@@ -10805,6 +10841,8 @@ node /org/freedesktop/systemd1/unit/system_2eslice {
GetProcesses(out a(sus) processes);
AttachProcesses(in s subcgroup,
in au pids);
RemoveSubgroup(in s subcgroup,
in t flags);
properties:
@org.freedesktop.DBus.Property.EmitsChangedSignal("false")
readonly s Slice = '...';
@@ -11004,6 +11042,8 @@ node /org/freedesktop/systemd1/unit/system_2eslice {
<!--method AttachProcesses is not documented!-->
<!--method RemoveSubgroup is not documented!-->
<!--property Slice is not documented!-->
<!--property ControlGroupId is not documented!-->
@@ -11196,6 +11236,8 @@ node /org/freedesktop/systemd1/unit/system_2eslice {
<variablelist class="dbus-method" generated="True" extra-ref="AttachProcesses()"/>
<variablelist class="dbus-method" generated="True" extra-ref="RemoveSubgroup()"/>
<variablelist class="dbus-property" generated="True" extra-ref="Slice"/>
<variablelist class="dbus-property" generated="True" extra-ref="ControlGroup"/>
@@ -11411,6 +11453,8 @@ node /org/freedesktop/systemd1/unit/session_2d1_2escope {
GetProcesses(out a(sus) processes);
AttachProcesses(in s subcgroup,
in au pids);
RemoveSubgroup(in s subcgroup,
in t flags);
signals:
RequestStop();
properties:
@@ -11636,6 +11680,8 @@ node /org/freedesktop/systemd1/unit/session_2d1_2escope {
<!--method AttachProcesses is not documented!-->
<!--method RemoveSubgroup is not documented!-->
<!--property RuntimeMaxUSec is not documented!-->
<!--property RuntimeRandomizedExtraUSec is not documented!-->
@@ -11850,6 +11896,8 @@ node /org/freedesktop/systemd1/unit/session_2d1_2escope {
<variablelist class="dbus-method" generated="True" extra-ref="AttachProcesses()"/>
<variablelist class="dbus-method" generated="True" extra-ref="RemoveSubgroup()"/>
<variablelist class="dbus-signal" generated="True" extra-ref="RequestStop()"/>
<variablelist class="dbus-property" generated="True" extra-ref="Controller"/>
@@ -12254,6 +12302,7 @@ $ gdbus introspect --system --dest org.freedesktop.systemd1 \
<varname>ShutdownStartTimestamp</varname>,
<varname>ShutdownStartTimestampMonotonic</varname>, and
<varname>SoftRebootsCount</varname> were added in version 256.</para>
<para><function>RemoveSubgroupFromUnit()</function> was added in version 258.</para>
</refsect2>
<refsect2>
<title>Unit Objects</title>
@@ -12320,7 +12369,7 @@ $ gdbus introspect --system --dest org.freedesktop.systemd1 \
<varname>ProtectControlGroupsEx</varname>,
<varname>PrivateUsersEx</varname>, and
<varname>PrivatePIDs</varname> were added in version 257.</para>
<para><varname>ProtectHostnameEx</varname> was added in version 258.</para>
<para><varname>ProtectHostnameEx</varname> and <function>RemoveSubGroup()</function> were added in version 258.</para>
</refsect2>
<refsect2>
<title>Socket Unit Objects</title>
@@ -12364,7 +12413,7 @@ $ gdbus introspect --system --dest org.freedesktop.systemd1 \
<varname>ManagedOOMMemoryPressureDurationUSec</varname>,
<varname>ProtectControlGroupsEx</varname>, and
<varname>PrivatePIDs</varname> were added in version 257.</para>
<para><varname>ProtectHostnameEx</varname> was added in version 258.</para>
<para><varname>ProtectHostnameEx</varname> and <function>RemoveSubgroup()</function> were added in version 258.</para>
</refsect2>
<refsect2>
<title>Mount Unit Objects</title>
@@ -12405,7 +12454,7 @@ $ gdbus introspect --system --dest org.freedesktop.systemd1 \
<varname>ManagedOOMMemoryPressureDurationUSec</varname>,
<varname>ProtectControlGroupsEx</varname>, and
<varname>PrivatePIDs</varname> were added in version 257.</para>
<para><varname>ProtectHostnameEx</varname> was added in version 258.</para>
<para><varname>ProtectHostnameEx</varname> and <function>RemoveSubgroup()</function> was added in version 258.</para>
</refsect2>
<refsect2>
<title>Swap Unit Objects</title>
@@ -12446,7 +12495,7 @@ $ gdbus introspect --system --dest org.freedesktop.systemd1 \
<varname>ManagedOOMMemoryPressureDurationUSec</varname>,
<varname>ProtectControlGroupsEx</varname>, and
<varname>PrivatePIDs</varname> were added in version 257.</para>
<para><varname>ProtectHostnameEx</varname> was added in version 258.</para>
<para><varname>ProtectHostnameEx</varname> and <function>RemoveSubgroup()</function> were added in version 258.</para>
</refsect2>
<refsect2>
<title>Slice Unit Objects</title>
@@ -12472,6 +12521,7 @@ $ gdbus introspect --system --dest org.freedesktop.systemd1 \
<varname>EffectiveTasksMax</varname>, and
<varname>MemoryZSwapWriteback</varname> were added in version 256.</para>
<para><varname>ManagedOOMMemoryPressureDurationUSec</varname> was added in version 257.</para>
<para><function>RemoveSubgroup()</function> was added in version 258.</para>
</refsect2>
<refsect2>
<title>Scope Unit Objects</title>
@@ -12498,6 +12548,7 @@ $ gdbus introspect --system --dest org.freedesktop.systemd1 \
<varname>EffectiveTasksMax</varname>, and
<varname>MemoryZSwapWriteback</varname> were added in version 256.</para>
<para><varname>ManagedOOMMemoryPressureDurationUSec</varname> was added in version 257.</para>
<para><function>RemoveSubgroup()</function> was added in version 258.</para>
</refsect2>
<refsect2>
<title>Job Objects</title>