Commit 08ce5f16 authored by Serge E. Hallyn's avatar Serge E. Hallyn Committed by Linus Torvalds

cgroups: implement device whitelist

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>
parent d447ea2f
Device Whitelist Controller
1. Description:
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 device
cgroup gets a copy of the parent. Administrators 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).
2. User Interface
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.
3. Security
Any task can move itself between cgroups. This clearly won't
suffice, but we can decide the best way to adequately restrict
movement as people get some experience with this. We may just want
to require CAP_SYS_ADMIN, which at least is a separate bit from
CAP_MKNOD. We may want to just refuse moving to a cgroup which
isn't a descendent of the current one. Or we may want to use
CAP_MAC_ADMIN, since we really are trying to lock down root.
CAP_SYS_ADMIN is needed to modify the whitelist or move another
task to a new cgroup. (Again we'll probably want to change that).
A cgroup may not be granted more permissions than the cgroup's
parent has.
......@@ -30,6 +30,7 @@
#include <linux/capability.h>
#include <linux/file.h>
#include <linux/fcntl.h>
#include <linux/device_cgroup.h>
#include <asm/namei.h>
#include <asm/uaccess.h>
......@@ -281,6 +282,10 @@ int permission(struct inode *inode, int mask, struct nameidata *nd)
if (retval)
return retval;
retval = devcgroup_inode_permission(inode, mask);
if (retval)
return retval;
return security_inode_permission(inode, mask, nd);
}
......@@ -2028,6 +2033,10 @@ int vfs_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t dev)
if (!dir->i_op || !dir->i_op->mknod)
return -EPERM;
error = devcgroup_inode_mknod(mode, dev);
if (error)
return error;
error = security_inode_mknod(dir, dentry, mode, dev);
if (error)
return error;
......
......@@ -42,3 +42,9 @@ SUBSYS(mem_cgroup)
#endif
/* */
#ifdef CONFIG_CGROUP_DEVICE
SUBSYS(devices)
#endif
/* */
#include <linux/module.h>
#include <linux/fs.h>
#ifdef CONFIG_CGROUP_DEVICE
extern int devcgroup_inode_permission(struct inode *inode, int mask);
extern int devcgroup_inode_mknod(int mode, dev_t dev);
#else
static inline int devcgroup_inode_permission(struct inode *inode, int mask)
{ return 0; }
static inline int devcgroup_inode_mknod(int mode, dev_t dev)
{ return 0; }
#endif
......@@ -298,6 +298,13 @@ config CGROUP_NS
for instance virtual servers and checkpoint/restart
jobs.
config CGROUP_DEVICE
bool "Device controller for cgroups"
depends on CGROUPS && EXPERIMENTAL
help
Provides a cgroup implementing whitelists for devices which
a process in the cgroup can mknod or open.
config CPUSETS
bool "Cpuset support"
depends on SMP && CGROUPS
......
......@@ -18,3 +18,4 @@ obj-$(CONFIG_SECURITY_SELINUX) += selinux/built-in.o
obj-$(CONFIG_SECURITY_SMACK) += commoncap.o smack/built-in.o
obj-$(CONFIG_SECURITY_CAPABILITIES) += commoncap.o capability.o
obj-$(CONFIG_SECURITY_ROOTPLUG) += commoncap.o root_plug.o
obj-$(CONFIG_CGROUP_DEVICE) += device_cgroup.o
This diff is collapsed.
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment