[arch-general] matrix-synapse "enhanced" security

[Patrick Pacher]

Hi,

First time responding here, if anything is not as it should please tell me.

I guess you should get it to work by creating a new drop-in file with
ReadWritePaths= set to the list of directories you want synapse to have
access to.
May consult the man page of systemd.exec for more information about that.

Best regards
Patrick

Uwe Sauter via arch-general <arch-general at lists.archlinux.org> schrieb am
Do., 18. Nov. 2021, 20:02:

> Dear all,
>
>
> beginning with matrix-synapse 1.44.0-1 in early October a Systemd override
> file (see below for reference) was included
> to the package that aims to enhance the security of Synapse. Amongst other
> things it tells Systemd to restrict access to
> certain directories that are seen as defaults.
>
> Unfortunately this enhancement broke my setup by neglecting that there are
> various paths inside Synapse's configuration
> that can be customized, e.g. media_store_path and uploads_path.
> The error I see in my logs is:
>
> 2021-11-18 19:54:30,772 - synapse.rest.media.v1.preview_url_resource - 559
> - WARNING - expire_url_cache_data-1281 -
> Failed to remove media directory:
> '/srv/matrix/media_store/url_cache/2021-10-08': [Errno 30] Read-only file
> system:
> '/srv/matrix/media_store/url_cache/2021-10-08'
> 2021-11-18 19:54:30,774 - synapse.rest.media.v1.preview_url_resource - 617
> - WARNING - expire_url_cache_data-1281 -
> Failed to remove media: '2021-10-08_cgWYZUYMTRBdzskW': [Errno 30]
> Read-only file system: '800-450-image-jpeg-scale'
>
> It is also impossible to insert pictures into the chat. The client just
> tells "unable to send message" but no log entry
> is created on the server.
>
>
> Did I miss any notification about this change?
>
> Can anyone help me with customizing the Systemd override file so that
> Synapse regains access to media_store_path and
> uploads_path?
>
> Any help is appreciated.
>
>
> Thank you,
>
>    Uwe
>
>
>
> ### /usr/lib/systemd/system/synapse.service.d/override-hardened.conf ###
> [Service]
> # The following directives give the synapse service R/W access to:
> # - /run/synapse
> # - /var/lib/synapse
> # - /var/log/synapse
>
> RuntimeDirectory=synapse
> StateDirectory=synapse
> LogsDirectory=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
> ### EOF ###
>