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90 lines
5.2 KiB
90 lines
5.2 KiB
2 years ago
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From 11f5677752f9b78239214b3064e5a2c3712d71b1 Mon Sep 17 00:00:00 2001
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From: Lennart Poettering <lennart@poettering.net>
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Date: Wed, 20 Mar 2019 20:19:38 +0100
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Subject: [PATCH] core: imply NNP and SUID/SGID restriction for DynamicUser=yes
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service
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Let's be safe, rather than sorry. This way DynamicUser=yes services can
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neither take benefit of, nor create SUID/SGID binaries.
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Given that DynamicUser= is a recent addition only we should be able to
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get away with turning this on, even though this is strictly speaking a
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binary compatibility breakage.
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(cherry picked from commit bf65b7e0c9fc215897b676ab9a7c9d1c688143ba)
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Resolves: #1687512
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---
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man/systemd.exec.xml | 16 ++++++++++------
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src/core/unit.c | 10 ++++++++--
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2 files changed, 18 insertions(+), 8 deletions(-)
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diff --git a/man/systemd.exec.xml b/man/systemd.exec.xml
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index 45ed1864f8..bdaed68162 100644
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--- a/man/systemd.exec.xml
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+++ b/man/systemd.exec.xml
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@@ -229,7 +229,9 @@
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created by the executed processes is bound to the runtime of the service, and hence the lifetime of the dynamic
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user/group. Since <filename>/tmp</filename> and <filename>/var/tmp</filename> are usually the only
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world-writable directories on a system this ensures that a unit making use of dynamic user/group allocation
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- cannot leave files around after unit termination. Moreover <varname>ProtectSystem=strict</varname> and
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+ cannot leave files around after unit termination. Furthermore <varname>NoNewPrivileges=</varname> and
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+ <varname>RestrictSUIDSGID=</varname> are implicitly enabled to ensure that processes invoked cannot take benefit
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+ or create SUID/SGID files or directories. Moreover <varname>ProtectSystem=strict</varname> and
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<varname>ProtectHome=read-only</varname> are implied, thus prohibiting the service to write to arbitrary file
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system locations. In order to allow the service to write to certain directories, they have to be whitelisted
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using <varname>ReadWritePaths=</varname>, but care must be taken so that UID/GID recycling doesn't create
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@@ -357,11 +359,12 @@ CapabilityBoundingSet=~CAP_B CAP_C</programlisting>
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<varname>RestrictAddressFamilies=</varname>, <varname>RestrictNamespaces=</varname>,
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<varname>PrivateDevices=</varname>, <varname>ProtectKernelTunables=</varname>,
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<varname>ProtectKernelModules=</varname>, <varname>MemoryDenyWriteExecute=</varname>,
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- <varname>RestrictRealtime=</varname>, <varname>RestrictSUIDSGID=</varname> or
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- <varname>LockPersonality=</varname> are specified. Note that even if this setting is overridden by
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- them, <command>systemctl show</command> shows the original value of this setting. Also see <ulink
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+ <varname>RestrictRealtime=</varname>, <varname>RestrictSUIDSGID=</varname>,
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+ <varname>DynamicUser=</varname> or <varname>LockPersonality=</varname> are specified. Note that even
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+ if this setting is overridden by them, <command>systemctl show</command> shows the original value of
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+ this setting. Also see <ulink
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url="https://www.kernel.org/doc/html/latest/userspace-api/no_new_privs.html">No New Privileges
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- Flag</ulink>. </para></listitem>
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+ Flag</ulink>.</para></listitem>
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</varlistentry>
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<varlistentry>
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@@ -1288,7 +1291,8 @@ RestrictNamespaces=~cgroup net</programlisting>
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identity of other users, it is recommended to restrict creation of SUID/SGID files to the few
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programs that actually require them. Note that this restricts marking of any type of file system
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object with these bits, including both regular files and directories (where the SGID is a different
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- meaning than for files, see documentation). Defaults to off.</para></listitem>
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+ meaning than for files, see documentation). This option is implied if <varname>DynamicUser=</varname>
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+ is enabled. Defaults to off.</para></listitem>
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</varlistentry>
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<varlistentry>
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diff --git a/src/core/unit.c b/src/core/unit.c
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index 115739f4c6..e1f5e6f7bd 100644
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--- a/src/core/unit.c
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+++ b/src/core/unit.c
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@@ -4161,14 +4161,20 @@ int unit_patch_contexts(Unit *u) {
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return -ENOMEM;
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}
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- /* If the dynamic user option is on, let's make sure that the unit can't leave its UID/GID
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- * around in the file system or on IPC objects. Hence enforce a strict sandbox. */
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+ /* If the dynamic user option is on, let's make sure that the unit can't leave its
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+ * UID/GID around in the file system or on IPC objects. Hence enforce a strict
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+ * sandbox. */
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ec->private_tmp = true;
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ec->remove_ipc = true;
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ec->protect_system = PROTECT_SYSTEM_STRICT;
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if (ec->protect_home == PROTECT_HOME_NO)
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ec->protect_home = PROTECT_HOME_READ_ONLY;
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+
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+ /* Make sure this service can neither benefit from SUID/SGID binaries nor create
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+ * them. */
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+ ec->no_new_privileges = true;
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+ ec->restrict_suid_sgid = true;
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}
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}
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