Quoting Pavel Emelyanov (xemul@xxxxxxxxxx): > Each new group will have its own maps for char and block > layers. The devices access list is tuned via the > devices.permissions file. One may read from the file to get > the configured state. > > The top container isn't initialized, so that the char > and block layers will use the global maps to lookup > their devices. I did that not to export the static maps > to the outer world. > > Good news is that this patch now contains more comments > and Documentation file :) Seems to work as advertised :) I can't reproduce Suka's null/zero bug. You're relying fully on uid-0 to stop writes into the devices.permissions files. Would you mind adding a check for CAP_SYS_ADMIN (or CAP_NS_OVERRIDE+CAP_MKNOD)? Or were you really counting on using the filesystem visibility cgroup to stop a container from making changes to its device access whitelist? thanks, -serge > Signed-off-by: Pavel Emelyanov <xemul@xxxxxxxxxx> > > --- > > diff --git a/Documentation/controllers/devices.txt b/Documentation/controllers/devices.txt > new file mode 100644 > index 0000000..dbd0c7a > --- /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. Grand 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@xxxxxxxxxx> > + > 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..48c5f69 > --- /dev/null > +++ b/fs/devscontrol.c > @@ -0,0 +1,314 @@ > +/* > + * devscontrol.c - Device Controller > + * > + * Copyright 2007 OpenVZ SWsoft 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 cgrous 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 onw 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 + 1; > +} > + > +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 228235c..9c0cd2c 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 > new file mode 100644 > index 0000000..38057b9 > --- /dev/null > +++ b/include/linux/devscontrol.h > @@ -0,0 +1,26 @@ > +#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 kobj_map *task_cdev_map(struct task_struct *tsk) > +{ > + return NULL; > +} > + > +static inline kobj_map *task_bdev_map(struct task_struct *tsk) > +{ > + return NULL; > +} > +#endif > +#endif > diff --git a/init/Kconfig b/init/Kconfig > index 732a1c2..f9a1b4f 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -283,6 +283,19 @@ 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 _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers