xfs_scrub_fail: tighten up the security on the background systemd service

Currently, xfs_scrub_fail has to run with enough privileges to access
the journal contents for a given scrub run and to send a report via
email.  Minimize the risk of xfs_scrub_fail escaping its service
container or contaminating the rest of the system by using systemd's
sandboxing controls to prohibit as much access as possible.

The directives added by this patch were recommended by the command
'systemd-analyze security xfs_scrub_fail@.service' in systemd 249.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

diff --git a/scrub/xfs_scrub_fail@.service.in b/scrub/xfs_scrub_fail@.service.in
index 32012ec353662e4e41ce143229b8b7804cb5e48e..2c879afd6d8eacfbac5b5b2f647e0c90d4290683 100644 (file)
--- a/scrub/xfs_scrub_fail@.service.in
+++ b/scrub/xfs_scrub_fail@.service.in
@@ -18,3 +18,58 @@ SupplementaryGroups=systemd-journal
 # Create the service underneath the scrub background service slice so that we
 # can control resource usage.
 Slice=system-xfs_scrub.slice
+
+# No realtime scheduling
+RestrictRealtime=true
+
+# Make the entire filesystem readonly and /home inaccessible.
+ProtectSystem=full
+ProtectHome=yes
+PrivateTmp=true
+RestrictSUIDSGID=true
+
+# Emailing reports requires network access, but not the ability to change the
+# hostname.
+ProtectHostname=true
+
+# Don't let the program mess with the kernel configuration at all
+ProtectKernelLogs=true
+ProtectKernelModules=true
+ProtectKernelTunables=true
+ProtectControlGroups=true
+ProtectProc=invisible
+RestrictNamespaces=true
+
+# Can't hide /proc because journalctl needs it to find various pieces of log
+# information
+#ProcSubset=pid
+
+# Only allow the default personality Linux
+LockPersonality=true
+
+# No writable memory pages
+MemoryDenyWriteExecute=true
+
+# Don't let our mounts leak out to the host
+PrivateMounts=true
+
+# Restrict system calls to the native arch and only enough to get things going
+SystemCallArchitectures=native
+SystemCallFilter=@system-service
+SystemCallFilter=~@privileged
+SystemCallFilter=~@resources
+SystemCallFilter=~@mount
+
+# xfs_scrub needs these privileges to run, and no others
+CapabilityBoundingSet=
+NoNewPrivileges=true
+
+# Failure reporting shouldn't create world-readable files
+UMask=0077
+
+# Clean up any IPC objects when this unit stops
+RemoveIPC=true
+
+# No access to hardware device files
+PrivateDevices=true
+ProtectClock=true