[PATCH 9/9] Devices accessibility control group itself

Pavel Emelyanov
2008-03-05T17:48:19Z

Finally, here's the control group, which makes full use of the
interfaces, declared in the previous patches.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>

---
Documentation/controllers/devices.txt | 61 +++++++
fs/Makefile | 2 +
fs/devscontrol.c | 314 +++++++++++++++++++++++++++++++++
include/linux/cgroup_subsys.h | 6 +
include/linux/devscontrol.h | 14 ++
init/Kconfig | 13 ++
6 files changed, 410 insertions(+), 0 deletions(-)
create mode 100644 Documentation/controllers/devices.txt
create mode 100644 fs/devscontrol.c

diff --git a/Documentation/controllers/devices.txt b/Documentation/controllers/devices.txt
new file mode 100644
index 0000000..630586c
--- /dev/null
+++ b/Documentation/controllers/devices.txt
@@ -0,0 +1,61 @@
+
+ Devices visibility controller
+
+This controller allows to tune the devices accessibility by tasks,
+i.e. grant full access for /dev/null, /dev/zero etc, grant read-only
+access to IDE devices and completely hide SCSI disks.
+
+Tasks still can call mknod to create device files, regardless of
+whether the particular device is visible or accessible, but they
+may not be able to open it later.
+
+This one hides under CONFIG_CGROUP_DEVS option.
+
+
+Configuring
+
+The controller provides a single file to configure itself -- the
+devices.permissions one. To change the accessibility level for some
+device write the following string into it:
+
+[cb] <major>:(<minor>|*) [r-][w-]
+ ^ ^ ^
+ | | |
+ | | +--- access rights (1)
+ | |
+ | +-- device major and minor numbers (2)
+ |
+ +-- device type (character / block)
+
+1) The access rights set to '--' remove the device from the group's
+access list, so that it will not even be shown in this file later.
+
+2) Setting the minor to '*' grants access to all the minors for
+particular major.
+
+When reading from it, one may see something like
+
+ c 1:5 rw
+ b 8:* r-
+
+Security issues, concerning who may grant access to what are governed
+at the cgroup infrastructure level.
+
+
+Examples:
+
+1. Grant full access to /dev/null
+ # echo 'c 1:3 rw' > /cgroups/<id>/devices.permissions
+
+2. Grant the read-only access to /dev/sda and partitions
+ # echo 'b 8:* r-' > ...
+
+3. Change the /dev/null access to write-only
+ # echo 'c 1:3 -w' > ...
+
+4. Revoke access to /dev/sda
+ # echo 'b 8:* --' > ...
+
+
+ Written by Pavel Emelyanov <xemul@openvz.org>
+
diff --git a/fs/Makefile b/fs/Makefile
index 7996220..5ad03be 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_CGROUP_DEVS) += devscontrol.o

# Do not add any filesystems before this line
obj-$(CONFIG_REISERFS_FS) += reiserfs/
diff --git a/fs/devscontrol.c b/fs/devscontrol.c
new file mode 100644
index 0000000..4a664cf
--- /dev/null
+++ b/fs/devscontrol.c
@@ -0,0 +1,314 @@
+/*
+ * devscontrol.c - Device Controller
+ *
+ * Copyright 2008 OpenVZ Parallels Inc
+ * Author: Pavel Emelyanov <xemul at openvz dot 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/cgroup.h>
+#include <linux/cdev.h>
+#include <linux/err.h>
+#include <linux/devscontrol.h>
+#include <linux/uaccess.h>
+#include <linux/fs.h>
+#include <linux/genhd.h>
+
+struct devs_cgroup {
+ /*
+ * The subsys state to build into cgroups infrastructure
+ */
+ struct cgroup_subsys_state css;
+
+ /*
+ * The maps of character and block devices. They provide a
+ * map from dev_t-s to struct cdev/gendisk. See fs/char_dev.c
+ * and block/genhd.c to find out how the ->open() callbacks
+ * work when opening a device.
+ *
+ * Each group will have its own maps, and at the open()
+ * time code will lookup in this map to get the device
+ * and permissions by its dev_t.
+ */
+ struct kobj_map *cdev_map;
+ struct kobj_map *bdev_map;
+};
+
+static inline
+struct devs_cgroup *css_to_devs(struct cgroup_subsys_state *css)
+{
+ return container_of(css, struct devs_cgroup, css);
+}
+
+static inline
+struct devs_cgroup *cgroup_to_devs(struct cgroup *cont)
+{
+ return css_to_devs(cgroup_subsys_state(cont, devs_subsys_id));
+}
+
+struct kobj_map *task_cdev_map(struct task_struct *tsk)
+{
+ struct cgroup_subsys_state *css;
+
+ css = task_subsys_state(tsk, devs_subsys_id);
+ if (css->cgroup->parent == NULL)
+ return NULL;
+ else
+ return css_to_devs(css)->cdev_map;
+}
+
+struct kobj_map *task_bdev_map(struct task_struct *tsk)
+{
+ struct cgroup_subsys_state *css;
+
+ css = task_subsys_state(tsk, devs_subsys_id);
+ if (css->cgroup->parent == NULL)
+ return NULL;
+ else
+ return css_to_devs(css)->bdev_map;
+}
+
+static struct cgroup_subsys_state *
+devs_create(struct cgroup_subsys *ss, struct cgroup *cont)
+{
+ struct devs_cgroup *devs;
+
+ devs = kzalloc(sizeof(struct devs_cgroup), GFP_KERNEL);
+ if (devs == NULL)
+ goto out;
+
+ devs->cdev_map = cdev_map_init();
+ if (devs->cdev_map == NULL)
+ goto out_free;
+
+ devs->bdev_map = bdev_map_init();
+ if (devs->bdev_map == NULL)
+ goto out_free_cdev;
+
+ return &devs->css;
+
+out_free_cdev:
+ cdev_map_fini(devs->cdev_map);
+out_free:
+ kfree(devs);
+out:
+ return ERR_PTR(-ENOMEM);
+}
+
+static void devs_destroy(struct cgroup_subsys *ss, struct cgroup *cont)
+{
+ struct devs_cgroup *devs;
+
+ devs = cgroup_to_devs(cont);
+ bdev_map_fini(devs->bdev_map);
+ cdev_map_fini(devs->cdev_map);
+ kfree(devs);
+}
+
+/*
+ * The devices.permissions file read/write functionality
+ *
+ * The following two routines parse and print the strings like
+ * [cb] <major>:(<minor>|*) [r-][w-]
+ */
+
+static int decode_perms_str(char *buf, int *chrdev, dev_t *dev,
+ int *all, mode_t *mode)
+{
+ unsigned int major, minor;
+ char *end;
+ mode_t tmp;
+
+ if (buf[0] == 'c')
+ *chrdev = 1;
+ else if (buf[0] == 'b')
+ *chrdev = 0;
+ else
+ return -EINVAL;
+
+ if (buf[1] != ' ')
+ return -EINVAL;
+
+ major = simple_strtoul(buf + 2, &end, 10);
+ if (*end != ':')
+ return -EINVAL;
+
+ if (end[1] == '*') {
+ if (end[2] != ' ')
+ return -EINVAL;
+
+ *all = 1;
+ minor = 0;
+ end += 2;
+ } else {
+ minor = simple_strtoul(end + 1, &end, 10);
+ if (*end != ' ')
+ return -EINVAL;
+
+ *all = 0;
+ }
+
+ tmp = 0;
+
+ if (end[1] == 'r')
+ tmp |= FMODE_READ;
+ else if (end[1] != '-')
+ return -EINVAL;
+ if (end[2] == 'w')
+ tmp |= FMODE_WRITE;
+ else if (end[2] != '-')
+ return -EINVAL;
+
+ *dev = MKDEV(major, minor);
+ *mode = tmp;
+ return 0;
+}
+
+static int encode_perms_str(char *buf, int len, int chrdev, dev_t dev,
+ int all, mode_t mode)
+{
+ int ret;
+
+ ret = snprintf(buf, len, "%c %d:", chrdev ? 'c' : 'b', MAJOR(dev));
+ if (all)
+ ret += snprintf(buf + ret, len - ret, "*");
+ else
+ ret += snprintf(buf + ret, len - ret, "%d", MINOR(dev));
+
+ ret += snprintf(buf + ret, len - ret, " %c%c\n",
+ (mode & FMODE_READ) ? 'r' : '-',
+ (mode & FMODE_WRITE) ? 'w' : '-');
+
+ return ret;
+}
+
+static ssize_t devs_write(struct cgroup *cont, struct cftype *cft,
+ struct file *f, const char __user *ubuf,
+ size_t nbytes, loff_t *pos)
+{
+ int err, all, chrdev;
+ dev_t dev;
+ char buf[64];
+ struct devs_cgroup *devs;
+ mode_t mode;
+
+ if (copy_from_user(buf, ubuf, sizeof(buf)))
+ return -EFAULT;
+
+ buf[sizeof(buf) - 1] = 0;
+ err = decode_perms_str(buf, &chrdev, &dev, &all, &mode);
+ if (err < 0)
+ return err;
+
+ devs = cgroup_to_devs(cont);
+
+ /*
+ * No locking here is required - all that we need
+ * is provided inside the kobject mapping code
+ */
+
+ if (mode == 0) {
+ if (chrdev)
+ err = cdev_del_from_map(devs->cdev_map, dev, all);
+ else
+ err = bdev_del_from_map(devs->bdev_map, dev, all);
+
+ if (err < 0)
+ return err;
+
+ css_put(&devs->css);
+ } else {
+ if (chrdev)
+ err = cdev_add_to_map(devs->cdev_map, dev, all, mode);
+ else
+ err = bdev_add_to_map(devs->bdev_map, dev, all, mode);
+
+ if (err < 0)
+ return err;
+
+ css_get(&devs->css);
+ }
+
+ return nbytes;
+}
+
+struct devs_dump_arg {
+ char *buf;
+ int pos;
+ int chrdev;
+};
+
+static int devs_dump_one(dev_t dev, int range, mode_t mode, void *x)
+{
+ struct devs_dump_arg *arg = x;
+ char tmp[64];
+ int len;
+
+ len = encode_perms_str(tmp, sizeof(tmp), arg->chrdev, dev,
+ range != 1, mode);
+
+ if (arg->pos >= PAGE_SIZE - len)
+ return 1;
+
+ memcpy(arg->buf + arg->pos, tmp, len);
+ arg->pos += len;
+ return 0;
+}
+
+static ssize_t devs_read(struct cgroup *cont, struct cftype *cft,
+ struct file *f, char __user *ubuf, size_t nbytes, loff_t *pos)
+{
+ struct devs_dump_arg arg;
+ struct devs_cgroup *devs;
+ ssize_t ret;
+
+ arg.buf = (char *)__get_free_page(GFP_KERNEL);
+ if (arg.buf == NULL)
+ return -ENOMEM;
+
+ devs = cgroup_to_devs(cont);
+ arg.pos = 0;
+
+ arg.chrdev = 1;
+ cdev_iterate_map(devs->cdev_map, devs_dump_one, &arg);
+
+ arg.chrdev = 0;
+ bdev_iterate_map(devs->bdev_map, devs_dump_one, &arg);
+
+ ret = simple_read_from_buffer(ubuf, nbytes, pos,
+ arg.buf, arg.pos);
+
+ free_page((unsigned long)arg.buf);
+ return ret;
+}
+
+static struct cftype devs_files[] = {
+ {
+ .name = "permissions",
+ .write = devs_write,
+ .read = devs_read,
+ },
+};
+
+static int devs_populate(struct cgroup_subsys *ss, struct cgroup *cont)
+{
+ return cgroup_add_files(cont, ss,
+ devs_files, ARRAY_SIZE(devs_files));
+}
+
+struct cgroup_subsys devs_subsys = {
+ .name = "devices",
+ .subsys_id = devs_subsys_id,
+ .create = devs_create,
+ .destroy = devs_destroy,
+ .populate = devs_populate,
+};
diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
index 1ddebfc..212c735 100644
--- a/include/linux/cgroup_subsys.h
+++ b/include/linux/cgroup_subsys.h
@@ -42,3 +42,9 @@ SUBSYS(mem_cgroup)
#endif

/* */
+
+#ifdef CONFIG_CGROUP_DEVS
+SUBSYS(devs)
+#endif
+
+/* */
diff --git a/include/linux/devscontrol.h b/include/linux/devscontrol.h
index 04c168b..ae5f801 100644
--- a/include/linux/devscontrol.h
+++ b/include/linux/devscontrol.h
@@ -1,5 +1,18 @@
#ifndef __DEVS_CONTROL_H__
#define __DEVS_CONTROL_H__
+struct kobj_map;
+struct task_struct;
+
+/*
+ * task_[cb]dev_map - get a map from task. Both calls may return
+ * NULL, to indicate, that task doesn't belong to any group and
+ * that the global map is to be used.
+ */
+
+#ifdef CONFIG_CGROUP_DEVS
+struct kobj_map *task_cdev_map(struct task_struct *);
+struct kobj_map *task_bdev_map(struct task_struct *);
+#else
static inline struct kobj_map *task_cdev_map(struct task_struct *tsk)
{
return NULL;
@@ -10,3 +23,4 @@ static inline struct kobj_map *task_bdev_map(struct task_struct *tsk)
return NULL;
}
#endif
+#endif
diff --git a/init/Kconfig b/init/Kconfig
index 77b2ac8..1b7e671 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -289,6 +289,19 @@ config CGROUP_DEBUG

Say N if unsure

+config CGROUP_DEVS
+ bool "Devices cgroup subsystem"
+ depends on CGROUPS
+ help
+ Controlls the access rights to devices, i.e. you may hide
+ some of them from tasks, so that they will not be able
+ to open them, or you may grant a read-only access to some
+ of them.
+
+ See Documentation/controllers/devices.txt for details.
+
+ This is harmless to say N here, so do it if unsure.
+
config CGROUP_NS
bool "Namespace cgroup subsystem"
depends on CGROUPS
--
1.5.3.4