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.
>
> Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Looks-good-to: Pavel Emelyanov <xemul@openvz.org>
> ---
> 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.
> + * 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)
> +{
> +
> + 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)
> +{
> + 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 entries */
> +/*
> + * called under cgroup_lock()
> + * since the list is visible to other tasks, we need the spinlock also
> + */
> +int dev_whit
...