Adopt capability drop explanations from other distros on Gentoo, drop…

… setpcap,sys_nice caps

Documents setpcap,sys_admin,sys_resources as breaking systemd, but does not drop them from lxc.cap.drop, as the default init system on Gentoo is OpenRC, thus stuff breaking systemd can be blocked anyway.

This also drops setpcap and sys_nice caps, as these are also dropped in other non-systemd distros.

Most of the explanatory blurb was copied from other distros' configs.

See-Also: https://bugs.gentoo.org/show_bug.cgi?id=551792

Signed-Off-By: Dennis Schridde <devurandom@gmx.net>

config/templates/gentoo.moresecure.conf.in

@@ -12,9 +12,26 @@ lxc.mount.entry=mqueue dev/mqueue mqueue rw,nodev,noexec,nosuid,create=dir 0 0
 lxc.mount.entry=shm dev/shm tmpfs rw,nosuid,nodev,noexec,relatime,create=dir 0 0
 lxc.mount.entry=run run tmpfs rw,nosuid,nodev,relatime,mode=755 0 0
 
-# this part is based on 'linux capabilities', see: man 7 capabilities
-#  eg: you may also wish to drop 'cap_net_raw' (though it breaks ping)
+# Capabilities
+# Uncomment these if you don't run anything that needs the capability, and
+# would like the container to run with less privilege.
 #
+# Dropping sys_admin disables container root from doing a lot of things
+# that could be bad like re-mounting lxc fstab entries rw for example,
+# but also disables some useful things like being able to nfs mount, and
+# things that are already namespaced with ns_capable() kernel checks, like
+# hostname(1).
+# lxc.cap.drop = sys_admin        # breaks systemd
+# lxc.cap.drop = net_raw          # breaks dhcp/ping
+# lxc.cap.drop = setgid           # breaks login (initgroups/setgroups)
+# lxc.cap.drop = dac_read_search  # breaks login (pam unix_chkpwd)
+# lxc.cap.drop = setuid           # breaks sshd,nfs statd
+# lxc.cap.drop = audit_control    # breaks sshd (set_loginuid failed)
+# lxc.cap.drop = audit_write
+# lxc.cap.drop = setpcap          # breaks journald
+# lxc.cap.drop = sys_resources    # breaks systemd
+lxc.cap.drop = audit_control audit_write dac_read_search fsetid ipc_owner linux_immutable mknod setfcap setpcap sys_admin sys_boot sys_nice sys_pacct sys_ptrace sys_rawio sys_resources sys_tty_config syslog
+
 # WARNING: the security vulnerability reported for 'cap_net_admin' at
 # http://mainisusuallyafunction.blogspot.com/2012/11/attacking-hardened-linux-systems-with.html
 # via JIT spraying (the BPF JIT module disabled on most systems was used
@@ -25,8 +42,3 @@ lxc.mount.entry=run run tmpfs rw,nosuid,nodev,relatime,mode=755 0 0
 # including the kernel - and multiple layers of security on any system
 # where security is a priority.  note that not only LXC but PAX (and
 # others?) were vulnerable to this issue.
-#
-# conservative: lxc.cap.drop = sys_module mknod mac_override sys_boot
-# aggressive follows. (leaves open: chown dac_override fowner ipc_lock kill lease net_admin net_bind_service net_broadcast net_raw setgid setuid sys_chroot)
-
-lxc.cap.drop = audit_control audit_write dac_read_search fsetid ipc_owner linux_immutable mknod setfcap sys_admin sys_boot sys_pacct sys_ptrace sys_rawio sys_resource sys_tty_config syslog