Serge E. Hallyn wrote:
> 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.
> 
> The parsing of devices.allow/deny needs to be cleaned up a bit and
> Documented.  I'd like to get an idea whether this approach is otherwise
> acceptable.
> 
> Changelog:
> 	Mar 17 2008: Place specific device cgroup hooks next to
> 		security_inode_{mknod,permission} rather than using
> 		the security hooks.
> 		Also remove most of the controls over tasks moving
> 		between cgroups and playing with the allow and deny
> 		permissions.
> 		Switch to major:minor format.
> 		Rename devcg to 'devices' to conform to cgroup naming.
> 	Mar 13 2008: move the dev_cgroup support into
> 		capability hooks instead of having it
> 		as a separate security module.
> 		Support root_plug with devcg.
> 		Note that due to this change, devcg will
> 		not be enforcing if the dummy module is
> 		loaded, or if selinux is loaded without
> 		capabilities.
> 	Mar 12 2008: allow dev_cgroup lsm to be used when
> 		SECURITY=n, and allow stacking with SELinux
> 		and Smack.  Don't work too hard in Kconfig
> 		to prevent a warning when smack+devcg are
> 		both compiled in, worry about that later.
> 

I would like to give some comments in the code. :)

> Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
> ---
>  fs/namei.c                    |    9 +
>  include/linux/cgroup_subsys.h |    6 +
>  include/linux/device_cgroup.h |   12 +
>  init/Kconfig                  |    7 +
>  security/Makefile             |    1 +
>  security/device_cgroup.c      |  597 +++++++++++++++++++++++++++++++++++++++++
>  6 files changed, 632 insertions(+), 0 deletions(-)
>  create mode 100644 include/linux/device_cgroup.h
>  create mode 100644 security/device_cgroup.c
> 
> diff --git a/fs/namei.c b/fs/namei.c
> index dfb3cb8..6caed32 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -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;
> diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
> index 1ddebfc..e287745 100644
> --- a/include/linux/cgroup_subsys.h
> +++ b/include/linux/cgroup_subsys.h
> @@ -42,3 +42,9 @@ SUBSYS(mem_cgroup)
>  #endif
>  
>  /* */
> +
> +#ifdef CONFIG_CGROUP_DEVICE
> +SUBSYS(devices)
> +#endif
> +
> +/* */
> diff --git a/include/linux/device_cgroup.h b/include/linux/device_cgroup.h
> new file mode 100644
> index 0000000..0b0d9c3
> --- /dev/null
> +++ b/include/linux/device_cgroup.h
> @@ -0,0 +1,12 @@
> +#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
> diff --git a/init/Kconfig b/init/Kconfig
> index 009f2d8..30868cd 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -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
> diff --git a/security/Makefile b/security/Makefile
> index 9e8b025..7ef1107 100644
> --- a/security/Makefile
> +++ b/security/Makefile
> @@ -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
> diff --git a/security/device_cgroup.c b/security/device_cgroup.c
> new file mode 100644
> index 0000000..33d8fd8
> --- /dev/null
> +++ b/security/device_cgroup.c
> @@ -0,0 +1,597 @@
> +/*
> + * dev_cgroup.c - device cgroup subsystem
> + *
> + * Copyright 2007 IBM Corp
> + */
> +
> +#include <linux/device_cgroup.h>
> +#include <linux/cgroup.h>
> +#include <linux/ctype.h>
> +#include <linux/list.h>
> +#include <asm/uaccess.h>
> +
> +#define ACC_MKNOD 1
> +#define ACC_READ  2
> +#define ACC_WRITE 4
> +#define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)
> +
> +#define DEV_BLOCK 1
> +#define DEV_CHAR  2
> +#define DEV_ALL   4  /* this represents all devices */
> +
> +/*
> + * whitelist locking rules:
> + * cgroup_lock() cannot be taken under cgroup->lock.

When you say cgroup->lock, you mean dev_cgroup->lock, right?
So would it be better to make it clear in the comment?

> + * cgroup->lock can be taken with or without cgroup_lock().
> + *
> + * modifications always require cgroup_lock
> + * modifications to a list which is visible require the
> + *   cgroup->lock *and* cgroup_lock()
> + * walking the list requires cgroup->lock or cgroup_lock().
> + *
> + * reasoning: dev_whitelist_copy() needs to kmalloc, so needs
> + *   a mutex, which the cgroup_lock() is.  Since modifying
> + *   a visible list requires both locks, either lock can be
> + *   taken for walking the list.  Since the wh->spinlock is taken
> + *   for modifying a public-accessible list, the spinlock is
> + *   sufficient for just walking the list.
> + */
> +
> +struct dev_whitelist_item {
> +	u32 major, minor;
> +	short type;
> +	short access;
> +	struct list_head list;
> +};
> +
> +struct dev_cgroup {
> +	struct cgroup_subsys_state css;
> +	struct list_head whitelist;
> +	spinlock_t lock;
> +};
> +
> +static inline struct dev_cgroup *cgroup_to_devcgroup(
> +		struct cgroup *cgroup)
> +{
> +	return container_of(cgroup_subsys_state(cgroup, devices_subsys_id),
> +			    struct dev_cgroup, css);
> +}
> +
> +
> +struct cgroup_subsys devices_subsys;
> +
> +static int devcgroup_can_attach(struct cgroup_subsys *ss,
> +		struct cgroup *new_cgroup, struct task_struct *task)
> +{
> +

redundant empty line

> +	if (current != task && !capable(CAP_SYS_ADMIN))
> +			return -EPERM;
> +
> +	return 0;
> +}
> +
> +/*
> + * called under cgroup_lock()
> + */
> +int dev_whitelist_copy(struct list_head *dest, struct list_head *orig)

static int

> +{
> +	struct dev_whitelist_item *wh, *tmp, *new;
> +
> +	list_for_each_entry(wh, orig, list) {
> +		new = kmalloc(sizeof(*wh), GFP_KERNEL);
> +		if (!new)
> +			goto free_and_exit;
> +		new->major = wh->major;
> +		new->minor = wh->minor;
> +		new->type = wh->type;
> +		new->access = wh->access;
> +		list_add_tail(&new->list, dest);
> +	}
> +
> +	return 0;
> +
> +free_and_exit:
> +	list_for_each_entry_safe(wh, tmp, dest, list) {
> +		list_del(&wh->list);
> +		kfree(wh);
> +	}
> +	return -ENOMEM;
> +}
> +
> +/* Stupid prototype - don't bother combining existing entrie