Improvements and fixes for systemd unbound.service

1. Remove `ProtectKernelTunables=true`: This prevents various with socket options from working as shown below.
`unbound[] warning: so-rcvbuf 1048576 was not granted. Got 425984. To fix: start with root permissions(linux) or sysctl bigger net.core.rmem_max(linux) or kern.ipc.maxsockbuf(bsd) values.`

2. Add `CAP_NET_ADMIN` to available caps which is needed for `ip-transparent: yes` config option to work as shown below.
`unbound[] warning: setsockopt(.. IP_TRANSPARENT ..) failed: Operation not permitted`

3. Make `ReadWritePaths` less permissive: `UNBOUND_SYSCONF_DIR` equals to `sysconfdir` which usually equals to `/etc` and `UNBOUND_LOCALSTATE_DIR` equals to `localstatedir` which usually equals to `/var`. Allowing write access for those dirs shouldn't be needed. The only dirs unbound should be allow to write to are `/run` ( for pidfile), `@UNBOUND_RUN_DIR@` (for chroot) and `@UNBOUND_CHROOT_DIR@` in case it differs from the previous one.

4. Bind-mount `/run/systemd/notify`, `UNBOUND_PIDFILE`, `/dev/log`, `/dev/urandom` in order to use them inside chroot.

5. Add few extra hardening options: `RestrictNamespaces`, `LockPersonality` and `RestrictSUIDSGID` should be safe to use.

diff --git a/contrib/unbound.service.in b/contrib/unbound.service.in
index 95976dd9425a536c4d8032cf12e1a36ca9704d77..5c512f1dc67cc2106ee091e34452aacd6863ac7b 100644 (file)
--- a/contrib/unbound.service.in
+++ b/contrib/unbound.service.in
@@ -13,7 +13,7 @@ ExecReload=/bin/kill -HUP $MAINPID
 ExecStart=@UNBOUND_SBIN_DIR@/unbound
 NotifyAccess=main
 Type=notify
-CapabilityBoundingSet=CAP_IPC_LOCK CAP_NET_BIND_SERVICE CAP_SETGID CAP_SETUID CAP_SYS_CHROOT CAP_SYS_RESOURCE
+CapabilityBoundingSet=CAP_IPC_LOCK CAP_NET_BIND_SERVICE CAP_SETGID CAP_SETUID CAP_SYS_CHROOT CAP_SYS_RESOURCE CAP_NET_ADMIN
 MemoryDenyWriteExecute=true
 NoNewPrivileges=true
 PrivateDevices=true
@@ -21,11 +21,18 @@ PrivateTmp=true
 ProtectHome=true
 ProtectControlGroups=true
 ProtectKernelModules=true
-ProtectKernelTunables=true
 ProtectSystem=strict
-ReadWritePaths=@UNBOUND_SYSCONF_DIR@ @UNBOUND_LOCALSTATE_DIR@ /run @UNBOUND_RUN_DIR@
+ReadWritePaths=/run @UNBOUND_RUN_DIR@ @UNBOUND_CHROOT_DIR@
+TemporaryFileSystem=@UNBOUND_CHROOT_DIR@/dev:ro
+TemporaryFileSystem=@UNBOUND_CHROOT_DIR@/run:ro
+BindReadOnlyPaths=-/run/systemd/notify:@UNBOUND_CHROOT_DIR@/run/systemd/notify
+BindPaths=-@UNBOUND_PIDFILE@:@UNBOUND_CHROOT_DIR@@UNBOUND_PIDFILE@
+BindReadOnlyPaths=-/dev/urandom:@UNBOUND_CHROOT_DIR@/dev/urandom
+BindPaths=-/dev/log:@UNBOUND_CHROOT_DIR@/dev/log
 RestrictAddressFamilies=AF_INET AF_INET6 AF_UNIX
 RestrictRealtime=true
 SystemCallArchitectures=native
 SystemCallFilter=~@clock @cpu-emulation @debug @keyring @module mount @obsolete @resources
-
+RestrictNamespaces=yes
+LockPersonality=yes
+RestrictSUIDSGID=yes