• Serge E. Hallyn's avatar
    cgroups: implement device whitelist · 08ce5f16
    Serge E. Hallyn authored
    Implement a cgroup to track and enforce open and mknod restrictions on device
    files.  A device cgroup associates a device access whitelist with each cgroup.
     A whitelist entry has 4 fields.  'type' is a (all), c (char), or b (block).
    'all' means it applies to all types and all major and minor numbers.  Major
    and minor are either an integer or * for all.  Access is a composition of r
    (read), w (write), and m (mknod).
    
    The root device cgroup starts with rwm to 'all'.  A child devcg gets a copy of
    the parent.  Admins can then remove devices from the whitelist or add new
    entries.  A child cgroup can never receive a device access which is denied its
    parent.  However when a device access is removed from a parent it will not
    also be removed from the child(ren).
    
    An entry is added using devices.allow, and removed using
    devices.deny.  For instance
    
    	echo 'c 1:3 mr' > /cgroups/1/devices.allow
    
    allows cgroup 1 to read and mknod the device usually known as
    /dev/null.  Doing
    
    	echo a > /cgroups/1/devices.deny
    
    will remove the default 'a *:* mrw' entry.
    
    CAP_SYS_ADMIN is needed to change permissions or move another task to a new
    cgroup.  A cgroup may not be granted more permissions than the cgroup's parent
    has.  Any task can move itself between cgroups.  This won't be sufficient, but
    we can decide the best way to adequately restrict movement later.
    
    [akpm@linux-foundation.org: coding-style fixes]
    [akpm@linux-foundation.org: fix may-be-used-uninitialized warning]
    Signed-off-by: default avatarSerge E. Hallyn <serue@us.ibm.com>
    Acked-by: default avatarJames Morris <jmorris@namei.org>
    Looks-good-to: Pavel Emelyanov <xemul@openvz.org>
    Cc: Daniel Hokka Zakrisson <daniel@hozac.com>
    Cc: Li Zefan <lizf@cn.fujitsu.com>
    Cc: Paul Menage <menage@google.com>
    Cc: Balbir Singh <balbir@in.ibm.com>
    Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    08ce5f16
device_cgroup.h 380 Bytes