use lxc.auto.mount to ensure proc and sys are readonly

Set lxc.auto.mount = proc:mixed in unprivilged mode. This ensures that lxc mounts sys and proc/sysrq-trigger as readonly.
Signed-off-by: Abin Shahab <ashahab@altiscale.com> (github: ashahab-altiscale)
Docker-DCO-1.1-Signed-off-by: Abin Shahab <ashahab@altiscale.com> (github: ashahab-altiscale)

daemon/execdriver/lxc/lxc_template.go

@@ -61,13 +61,24 @@ lxc.cgroup.devices.allow = {{$allowedDevice.GetCgroupAllowString}}
 lxc.pivotdir = lxc_putold
 
 # NOTICE: These mounts must be applied within the namespace
-
+{{if .ProcessConfig.Privileged}}
 # WARNING: mounting procfs and/or sysfs read-write is a known attack vector.
 # See e.g. http://blog.zx2c4.com/749 and http://bit.ly/T9CkqJ
 # We mount them read-write here, but later, dockerinit will call the Restrict() function to remount them read-only.
 # We cannot mount them directly read-only, because that would prevent loading AppArmor profiles.
 lxc.mount.entry = proc {{escapeFstabSpaces $ROOTFS}}/proc proc nosuid,nodev,noexec 0 0
 lxc.mount.entry = sysfs {{escapeFstabSpaces $ROOTFS}}/sys sysfs nosuid,nodev,noexec 0 0
+	{{if .AppArmor}}
+lxc.aa_profile = unconfined
+	{{end}}
+{{else}}
+# In non-privileged mode, lxc will automatically mount /proc and /sys in readonly mode
+# for security. See: http://man7.org/linux/man-pages/man5/lxc.container.conf.5.html
+lxc.mount.auto = proc sys
+	{{if .AppArmor}}
+lxc.aa_profile = .AppArmorProfile
+	{{end}}
+{{end}}
 
 {{if .ProcessConfig.Tty}}
 lxc.mount.entry = {{.ProcessConfig.Console}} {{escapeFstabSpaces $ROOTFS}}/dev/console none bind,rw 0 0
@@ -85,14 +96,6 @@ lxc.mount.entry = {{$value.Source}} {{escapeFstabSpaces $ROOTFS}}/{{escapeFstabS
 {{end}}
 {{end}}
 
-{{if .ProcessConfig.Privileged}}
-{{if .AppArmor}}
-lxc.aa_profile = unconfined
-{{else}}
-# Let AppArmor normal confinement take place (i.e., not unconfined)
-{{end}}
-{{end}}
-
 # limits
 {{if .Resources}}
 {{if .Resources.Memory}}