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

Documentation/controllers/devices.txt

0 → 100644
+48 −0
Original line number Diff line number Diff line 
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.

fs/namei.c

+9 −0
Original line number Diff line number Diff line
@@ -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;

include/linux/cgroup_subsys.h

+6 −0
Original line number Diff line number Diff line
@@ -42,3 +42,9 @@ SUBSYS(mem_cgroup) 
#endif



/* */



#ifdef CONFIG_CGROUP_DEVICE

SUBSYS(devices)

#endif



/* */

include/linux/device_cgroup.h

0 → 100644
+12 −0
Original line number Diff line number Diff line 
#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

init/Kconfig

+7 −0
Original line number Diff line number Diff line
@@ -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

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