Hardened systemd unit files (#9803)

Signed-off-by: Savyasachee Jha <savya.jha@hawkradius.com>

changelog.d/9803.doc

+Add hardened systemd files as proposed in [#9760](https://github.com/matrix-org/synapse/issues/9760) and added them to `contrib/`. Change the docs to reflect the presence of these files.

contrib/systemd/override-hardened.conf

+[Service]
+# The following directives give the synapse service R/W access to:
+# - /run/matrix-synapse
+# - /var/lib/matrix-synapse
+# - /var/log/matrix-synapse
+
+RuntimeDirectory=matrix-synapse
+StateDirectory=matrix-synapse
+LogsDirectory=matrix-synapse
+
+######################
+## Security Sandbox ##
+######################
+
+# Make sure that the service has its own unshared tmpfs at /tmp and that it
+# cannot see or change any real devices
+PrivateTmp=true
+PrivateDevices=true
+
+# We give no capabilities to a service by default
+CapabilityBoundingSet=
+AmbientCapabilities=
+
+# Protect the following from modification:
+# - The entire filesystem
+# - sysctl settings and loaded kernel modules
+# - No modifications allowed to Control Groups
+# - Hostname
+# - System Clock
+ProtectSystem=strict
+ProtectKernelTunables=true
+ProtectKernelModules=true
+ProtectControlGroups=true
+ProtectClock=true
+ProtectHostname=true
+
+# Prevent access to the following:
+# - /home directory
+# - Kernel logs
+ProtectHome=tmpfs
+ProtectKernelLogs=true
+
+# Make sure that the process can only see PIDs and process details of itself,
+# and the second option disables seeing details of things like system load and
+# I/O etc
+ProtectProc=invisible
+ProcSubset=pid
+
+# While not needed, we set these options explicitly
+# - This process has been given access to the host network
+# - It can also communicate with any IP Address
+PrivateNetwork=false
+RestrictAddressFamilies=AF_INET AF_INET6 AF_UNIX
+IPAddressAllow=any
+
+# Restrict system calls to a sane bunch
+SystemCallArchitectures=native
+SystemCallFilter=@system-service
+SystemCallFilter=~@privileged @resources @obsolete
+
+# Misc restrictions
+# - Since the process is a python process it needs to be able to write and
+#   execute memory regions, so we set MemoryDenyWriteExecute to false
+RestrictSUIDSGID=true
+RemoveIPC=true
+NoNewPrivileges=true
+RestrictRealtime=true
+RestrictNamespaces=true
+LockPersonality=true
+PrivateUsers=true
+MemoryDenyWriteExecute=false

docs/systemd-with-workers/README.md

@@ -65,3 +65,33 @@ systemctl restart matrix-synapse-worker@federation_reader.service
 systemctl enable matrix-synapse-worker@federation_writer.service
 systemctl restart matrix-synapse.target
 ```
+
+## Hardening
+
+**Optional:** If further hardening is desired, the file
+`override-hardened.conf` may be copied from
+`contrib/systemd/override-hardened.conf` in this repository to the location
+`/etc/systemd/system/matrix-synapse.service.d/override-hardened.conf` (the
+directory may have to be created). It enables certain sandboxing features in
+systemd to further secure the synapse service. You may read the comments to
+understand what the override file is doing. The same file will need to be copied
+to
+`/etc/systemd/system/matrix-synapse-worker@.service.d/override-hardened-worker.conf`
+(this directory may also have to be created) in order to apply the same
+hardening options to any worker processes.
+
+Once these files have been copied to their appropriate locations, simply reload
+systemd's manager config files and restart all Synapse services to apply the hardening options. They will automatically
+be applied at every restart as long as the override files are present at the
+specified locations.
+
+```sh
+systemctl daemon-reload
+
+# Restart services
+systemctl restart matrix-synapse.target
+```
+
+In order to see their effect, you may run `systemd-analyze security
+matrix-synapse.service` before and after applying the hardening options to see
+the changes being applied at a glance.