[Devel] Re: [RFC][PATCH] Devices visibility container
Serge E. Hallyn
serue at us.ibm.com
Mon Sep 24 07:39:15 PDT 2007
Quoting Pavel Emelyanov (xemul at openvz.org):
> Hi.
>
> At KS we have pointed out the need in some container, that allows
> to limit the visibility of some devices to task within it. I.e.
> allow for /dev/null, /dev/zero etc, but disable (by default) some
> IDE devices or SCSI discs and so on.
>
> Here's the beta of the container. Currently this only allows to
> hide the _character_ devices only from the living tasks. To play
> with it you just create the container like this
>
> # mount -t container none /cont/devs -o devices
> # mkdir /cont/devs/0
>
> it will have two specific files
>
> # ls /cont/devs
> devices.block devices.char notify_on_release releasable release_agent tasks
>
> then move a task into it
>
> # /bin/echo -n $$ > /cont/devs/0/tasks
>
> after this you won't be able to read from even /dev/zero
>
> # hexdump /dev/zero
> hexdump: /dev/zero: No such device or address
> hexdump: /dev/zero: Bad file descriptor
>
> meanwhile from another ssh session you will. You may allow access
> to /dev/zero like this
>
> # /bin/echo -n '+1:5' > /cont/devs/0/devices.char
>
> More generally, the '+<major>:<minor>' string grants access to
> some device, and '-<major>:<minor>' disables one.
>
> The TODO list now looks like this:
> * add the block devices support :) don't know how to make it yet;
> * make /proc/devices show relevant info depending on who is
> reading it. currently even if major 1 is disabled for task,
> it will be listed in this file;
> * make it possible to enable/disable not just individual major:minor
> pair, but something more flexible, e.g. major:* for all minors
> for given major or major:m1-m2 for minor range, etc;
> * add the ability to restrict the read/write permissions for a
> container. currently one may just control the visible-invisible
> state for a device in a container, but maybe just readable or
> just writable would be better.
>
> This patch is minimally tested, because I just want to know your
> opinion on whether it worths developing the container in such a way or not.
Hmm,
I was thinking we would use LSM for this. Mostly it should suffice
to set up a reasonable /dev for the container to start with, and
hook security_mknod() to prevent it creating devices not on it's
whitelist. If deemed necessary, read/write could be controlled
by hooking security_permission() and checking whether
file->f_path.dentry->d_inode is a device on the read or write
whitelist.
It would still be a device controller, so it can be composed with an
ns_proxy controller, and the whitelist is modified using the
devs_controller.whitelist file, but it registers a security_ops
with these two hooks.
I haven't implemented that yet, though, whereas you already have code :)
As for handling blkdevs with your code, would just hooking
fs/block_dev.c:do_open() not work? Or is that not what you are
asking?
thanks,
-serge
> Signed-off-by: Pavel Emelyanov <xemul at openvz.org>
>
> ---
>
> diff --git a/drivers/base/map.c b/drivers/base/map.c
> index e87017f..0188053 100644
> --- a/drivers/base/map.c
> +++ b/drivers/base/map.c
> @@ -153,3 +153,21 @@ struct kobj_map *kobj_map_init(kobj_prob
> p->lock = lock;
> return p;
> }
> +
> +void kobj_map_fini(struct kobj_map *map)
> +{
> + int i;
> + struct probe *p, *next;
> +
> + for (i = 0; i < 256; i++) {
> + p = map->probes[i];
> + while (p->next != NULL) {
> + next = p->next;
> + kfree(p);
> + p = next;
> + }
> + }
> +
> + kfree(p);
> + kfree(map);
> +}
> diff --git a/fs/Makefile b/fs/Makefile
> index 2661ef9..837c731 100644
> --- a/fs/Makefile
> +++ b/fs/Makefile
> @@ -64,6 +64,8 @@ obj-y += devpts/
>
> obj-$(CONFIG_PROFILING) += dcookies.o
> obj-$(CONFIG_DLM) += dlm/
> +
> +obj-$(CONFIG_CONTAINER_DEVS) += devscontrol.o
>
> # Do not add any filesystems before this line
> obj-$(CONFIG_REISERFS_FS) += reiserfs/
> diff --git a/fs/char_dev.c b/fs/char_dev.c
> index c3bfa76..1b0e4da 100644
> --- a/fs/char_dev.c
> +++ b/fs/char_dev.c
> @@ -22,6 +22,8 @@
> #include <linux/mutex.h>
> #include <linux/backing-dev.h>
>
> +#include <linux/devscontrol.h>
> +
> #ifdef CONFIG_KMOD
> #include <linux/kmod.h>
> #endif
> @@ -362,17 +364,24 @@ int chrdev_open(struct inode * inode, st
> struct cdev *p;
> struct cdev *new = NULL;
> int ret = 0;
> + struct kobj_map *map;
> +
> + map = task_cdev_map(current);
> + if (map == NULL)
> + map = cdev_map;
>
> spin_lock(&cdev_lock);
> p = inode->i_cdev;
> - if (!p) {
> + if (!p || p->last != map) {
> struct kobject *kobj;
> int idx;
> +
> spin_unlock(&cdev_lock);
> - kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
> + kobj = kobj_lookup(map, inode->i_rdev, &idx);
> if (!kobj)
> return -ENXIO;
> new = container_of(kobj, struct cdev, kobj);
> + BUG_ON(p != NULL && p != new);
> spin_lock(&cdev_lock);
> p = inode->i_cdev;
> if (!p) {
> @@ -384,6 +393,8 @@ int chrdev_open(struct inode * inode, st
> ret = -ENXIO;
> } else if (!cdev_get(p))
> ret = -ENXIO;
> + if (p)
> + p->last = map;
> spin_unlock(&cdev_lock);
> cdev_put(new);
> if (ret)
> @@ -461,6 +472,49 @@ int cdev_add(struct cdev *p, dev_t dev,
> return kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p);
> }
>
> +int cdev_add_to_map(struct kobj_map *map, dev_t dev)
> +{
> + int tmp;
> + struct kobject *k;
> + struct cdev *c;
> +
> + k = kobj_lookup(cdev_map, dev, &tmp);
> + if (k == NULL)
> + return -ENODEV;
> +
> + c = container_of(k, struct cdev, kobj);
> + tmp = kobj_map(map, dev, 1, NULL, exact_match, exact_lock, c);
> + if (tmp < 0) {
> + cdev_put(c);
> + return tmp;
> + }
> +
> + return 0;
> +}
> +
> +int cdev_del_from_map(struct kobj_map *map, dev_t dev)
> +{
> + int tmp;
> + struct kobject *k;
> + struct cdev *c;
> +
> + k = kobj_lookup(cdev_map, dev, &tmp);
> + if (k == NULL)
> + return -ENODEV;
> +
> + c = container_of(k, struct cdev, kobj);
> + kobj_unmap(map, dev, 1);
> +
> + spin_lock(&cdev_lock);
> + if (c->last == map)
> + c->last = NULL;
> + spin_unlock(&cdev_lock);
> +
> + cdev_put(c);
> + cdev_put(c);
> + return 0;
> +}
> +
> static void cdev_unmap(dev_t dev, unsigned count)
> {
> kobj_unmap(cdev_map, dev, count);
> @@ -542,6 +596,16 @@ static struct kobject *base_probe(dev_t
> return NULL;
> }
>
> +struct kobj_map *cdev_map_init(void)
> +{
> + return kobj_map_init(base_probe, &chrdevs_lock);
> +}
> +
> +void cdev_map_fini(struct kobj_map *map)
> +{
> + kobj_map_fini(map);
> +}
> +
> void __init chrdev_init(void)
> {
> cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
> diff --git a/fs/devscontrol.c b/fs/devscontrol.c
> new file mode 100644
> index 0000000..6fb5f05
> --- /dev/null
> +++ b/fs/devscontrol.c
> @@ -0,0 +1,170 @@
> +/*
> + * devscontrol.c - Device Controller
> + *
> + * Copyright 2007 OpenVZ SWsoft Inc
> + * Author: Pavel Emelyanov <xemul at openvz.org>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + */
> +
> +#include <linux/container.h>
> +#include <linux/cdev.h>
> +#include <linux/err.h>
> +#include <linux/devscontrol.h>
> +#include <linux/uaccess.h>
> +
> +struct devs_container {
> + struct container_subsys_state css;
> +
> + struct kobj_map *cdev_map;
> +};
> +
> +static inline
> +struct devs_container *css_to_devs(struct container_subsys_state *css)
> +{
> + return container_of(css, struct devs_container, css);
> +}
> +
> +static inline
> +struct devs_container *container_to_devs(struct container *cont)
> +{
> + return css_to_devs(container_subsys_state(cont, devs_subsys_id));
> +}
> +
> +struct kobj_map *task_cdev_map(struct task_struct *tsk)
> +{
> + struct container_subsys_state *css;
> +
> + css = task_subsys_state(tsk, devs_subsys_id);
> + if (css->container->parent == NULL)
> + return NULL;
> + else
> + return css_to_devs(css)->cdev_map;
> +}
> +
> +static struct container_subsys_state *
> +devs_create(struct container_subsys *ss, struct container *cont)
> +{
> + struct devs_container *devs;
> +
> + devs = kzalloc(sizeof(struct devs_container), GFP_KERNEL);
> + if (devs == NULL)
> + goto out;
> +
> + devs->cdev_map = cdev_map_init();
> + if (devs->cdev_map == NULL)
> + goto out_free;
> +
> + return &devs->css;
> +
> +out_free:
> + kfree(devs);
> +out:
> + return ERR_PTR(-ENOMEM);
> +}
> +
> +static void devs_destroy(struct container_subsys *ss, struct container *cont)
> +{
> + struct devs_container *devs;
> +
> + devs = container_to_devs(cont);
> + cdev_map_fini(devs->cdev_map);
> + kfree(devs);
> +}
> +
> +static int decode_dev_name(char *buf, dev_t *dev)
> +{
> + unsigned int major, minor;
> + char *end;
> +
> + major = simple_strtoul(buf, &end, 10);
> + if (*end != ':')
> + return -EINVAL;
> +
> + minor = simple_strtoul(end + 1, &end, 10);
> + if (*end != '\0')
> + return -EINVAL;
> +
> + *dev = MKDEV(major, minor);
> + return 0;
> +}
> +
> +static ssize_t
> +devs_char_write(struct container *cont, struct cftype *cft, struct file *f,
> + const char __user *userbuf, size_t nbytes, loff_t *pos)
> +{
> + int err;
> + dev_t dev;
> + char buf[64];
> + struct devs_container *devs;
> +
> + if (copy_from_user(buf, userbuf, sizeof(buf)))
> + return -EFAULT;
> +
> + err = decode_dev_name(buf + 1, &dev);
> + if (err < 0)
> + return err;
> +
> + devs = container_to_devs(cont);
> +
> + switch (buf[0]) {
> + case '+':
> + err = cdev_add_to_map(devs->cdev_map, dev);
> + if (err < 0)
> + return err;
> +
> + css_get(&devs->css);
> + break;
> + case '-':
> + err = cdev_del_from_map(devs->cdev_map, dev);
> + if (err < 0)
> + return err;
> +
> + css_put(&devs->css);
> + break;
> + default:
> + return -EINVAL;
> + }
> +
> + return nbytes;
> +}
> +
> +static ssize_t
> +devs_block_write(struct container *cont, struct cftype *cft, struct file *f,
> + const char __user *userbuf, size_t nbytes, loff_t *pos)
> +{
> + return -ENOTTY;
> +}
> +
> +static struct cftype devs_files[] = {
> + {
> + .name = "char",
> + .write = devs_char_write,
> + },
> + {
> + .name = "block",
> + .write = devs_block_write,
> + },
> +};
> +
> +static int devs_populate(struct container_subsys *ss, struct container *cont)
> +{
> + return container_add_files(cont, ss,
> + devs_files, ARRAY_SIZE(devs_files));
> +}
> +
> +struct container_subsys devs_subsys = {
> + .name = "devices",
> + .subsys_id = devs_subsys_id,
> + .create = devs_create,
> + .destroy = devs_destroy,
> + .populate = devs_populate,
> +};
> diff --git a/include/linux/cdev.h b/include/linux/cdev.h
> index 1e29b13..0eded40 100644
> --- a/include/linux/cdev.h
> +++ b/include/linux/cdev.h
> @@ -9,6 +9,7 @@
> struct file_operations;
> struct inode;
> struct module;
> +struct kobj_map;
>
> struct cdev {
> struct kobject kobj;
> @@ -17,6 +18,7 @@ struct cdev {
> struct list_head list;
> dev_t dev;
> unsigned int count;
> + struct kobj_map *last;
> };
>
> void cdev_init(struct cdev *, const struct file_operations *);
> @@ -33,5 +35,9 @@ void cd_forget(struct inode *);
>
> extern struct backing_dev_info directly_mappable_cdev_bdi;
>
> +int cdev_add_to_map(struct kobj_map *map, dev_t dev);
> +int cdev_del_from_map(struct kobj_map *map, dev_t dev);
> +struct kobj_map *cdev_map_init(void);
> +void cdev_map_fini(struct kobj_map *map);
> #endif
> #endif
> diff --git a/include/linux/container_subsys.h b/include/linux/container_subsys.h
> index 81d11c2..9315a9b 100644
> --- a/include/linux/container_subsys.h
> +++ b/include/linux/container_subsys.h
> @@ -36,3 +36,9 @@ SUBSYS(mem_container)
> #endif
>
> /* */
> +
> +#ifdef CONFIG_CONTAINER_DEVS
> +SUBSYS(devs)
> +#endif
> +
> +/* */
> diff --git a/include/linux/devscontrol.h b/include/linux/devscontrol.h
> new file mode 100644
> index 0000000..51ae916
> --- /dev/null
> +++ b/include/linux/devscontrol.h
> @@ -0,0 +1,14 @@
> +#ifndef __DEVS_CONTROL_H__
> +#define __DEVS_CONTROL_H__
> +struct kobj_map;
> +struct task_struct;
> +
> +#ifdef CONFIG_CONTAINER_DEVS
> +struct kobj_map *task_cdev_map(struct task_struct *);
> +#else
> +static inline kobj_map *task_cdev_map(struct task_struct *tsk)
> +{
> + return NULL;
> +}
> +#endif
> +#endif
> diff --git a/include/linux/kobj_map.h b/include/linux/kobj_map.h
> index bafe178..2476f8d 100644
> --- a/include/linux/kobj_map.h
> +++ b/include/linux/kobj_map.h
> @@ -10,5 +10,6 @@ int kobj_map(struct kobj_map *, dev_t, u
> void kobj_unmap(struct kobj_map *, dev_t, unsigned long);
> struct kobject *kobj_lookup(struct kobj_map *, dev_t, int *);
> struct kobj_map *kobj_map_init(kobj_probe_t *, struct mutex *);
> +void kobj_map_fini(struct kobj_map *);
>
> #endif
> diff --git a/init/Kconfig b/init/Kconfig
> index 0bb211a..5e1158e 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -292,6 +292,12 @@ config CONTAINER_DEBUG
>
> Say N if unsure
>
> +config CONTAINER_DEVS
> + bool "Devices container subsystem"
> + depends on CONTAINERS
> + help
> + Controlls the visibility of devices
> +
> config CONTAINER_NS
> bool "Namespace container subsystem"
> depends on CONTAINERS
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