diff options
| -rw-r--r-- | Documentation/controllers/devices.txt | 48 | ||||
| -rw-r--r-- | fs/namei.c | 9 | ||||
| -rw-r--r-- | include/linux/cgroup_subsys.h | 6 | ||||
| -rw-r--r-- | include/linux/device_cgroup.h | 12 | ||||
| -rw-r--r-- | init/Kconfig | 7 | ||||
| -rw-r--r-- | security/Makefile | 1 | ||||
| -rw-r--r-- | security/device_cgroup.c | 603 |
7 files changed, 686 insertions, 0 deletions
diff --git a/Documentation/controllers/devices.txt b/Documentation/controllers/devices.txt new file mode 100644 index 00000000000..4dcea42432c --- /dev/null +++ b/Documentation/controllers/devices.txt @@ -0,0 +1,48 @@ +Device Whitelist Controller + +1. Description: + +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 device +cgroup gets a copy of the parent. Administrators 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). + +2. User Interface + +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. + +3. Security + +Any task can move itself between cgroups. This clearly won't +suffice, but we can decide the best way to adequately restrict +movement as people get some experience with this. We may just want +to require CAP_SYS_ADMIN, which at least is a separate bit from +CAP_MKNOD. We may want to just refuse moving to a cgroup which +isn't a descendent of the current one. Or we may want to use +CAP_MAC_ADMIN, since we really are trying to lock down root. + +CAP_SYS_ADMIN is needed to modify the whitelist or move another +task to a new cgroup. (Again we'll probably want to change that). + +A cgroup may not be granted more permissions than the cgroup's +parent has. diff --git a/fs/namei.c b/fs/namei.c index e179f71bfcb..32fd9655485 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 1ddebfc5256..e2877454ec8 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 00000000000..0b0d9c39ed6 --- /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 6ce16bdbec7..a3457926342 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 9e8b0252501..7ef1107a728 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 00000000000..4237b19e8fb --- /dev/null +++ b/security/device_cgroup.c @@ -0,0 +1,603 @@ +/* + * 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 <linux/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 dev_cgroup->lock. + * dev_cgroup->lock can be taken with or without cgroup_lock(). + * + * modifications always require cgroup_lock + * modifications to a list which is visible require the + * dev_cgroup->lock *and* cgroup_lock() + * walking the list requires dev_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. + */ + +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() + */ +static 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 + */ +static int dev_whitelist_add(struct dev_cgroup *dev_cgroup, + struct dev_whitelist_item *wh) +{ + struct dev_whitelist_item *whcopy; + + whcopy = kmalloc(sizeof(*whcopy), GFP_KERNEL); + if (!whcopy) + return -ENOMEM; + + memcpy(whcopy, wh, sizeof(*whcopy)); + spin_lock(&dev_cgroup->lock); + list_add_tail(&whcopy->list, &dev_cgroup->whitelist); + spin_unlock(&dev_cgroup->lock); + return 0; +} + +/* + * called under cgroup_lock() + * since the list is visible to other tasks, we need the spinlock also + */ +static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup, + struct dev_whitelist_item *wh) +{ + struct dev_whitelist_item *walk, *tmp; + + spin_lock(&dev_cgroup->lock); + list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) { + if (walk->type == DEV_ALL) + goto remove; + if (walk->type != wh->type) + continue; + if (walk->major != ~0 && walk->major != wh->major) + continue; + if (walk->minor != ~0 && walk->minor != wh->minor) + continue; + +remove: + walk->access &= ~wh->access; + if (!walk->access) { + list_del(&walk->list); + kfree(walk); + } + } + spin_unlock(&dev_cgroup->lock); +} + +/* + * called from kernel/cgroup.c with cgroup_lock() held. + */ +static struct cgroup_subsys_state *devcgroup_create(struct cgroup_subsys *ss, + struct cgroup *cgroup) +{ + struct dev_cgroup *dev_cgroup, *parent_dev_cgroup; + struct cgroup *parent_cgroup; + int ret; + + dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL); + if (!dev_cgroup) + return ERR_PTR(-ENOMEM); + INIT_LIST_HEAD(&dev_cgroup->whitelist); + parent_cgroup = cgroup->parent; + + if (parent_cgroup == NULL) { + struct dev_whitelist_item *wh; + wh = kmalloc(sizeof(*wh), GFP_KERNEL); + if (!wh) { + kfree(dev_cgroup); + return ERR_PTR(-ENOMEM); + } + wh->minor = wh->major = ~0; + wh->type = DEV_ALL; + wh->access = ACC_MKNOD | ACC_READ | ACC_WRITE; + list_add(&wh->list, &dev_cgroup->whitelist); + } else { + parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup); + ret = dev_whitelist_copy(&dev_cgroup->whitelist, + &parent_dev_cgroup->whitelist); + if (ret) { + kfree(dev_cgroup); + return ERR_PTR(ret); + } + } + + spin_lock_init(&dev_cgroup->lock); + return &dev_cgroup->css; +} + +static void devcgroup_destroy(struct cgroup_subsys *ss, + struct cgroup *cgroup) +{ + struct dev_cgroup *dev_cgroup; + struct dev_whitelist_item *wh, *tmp; + + dev_cgroup = cgroup_to_devcgroup(cgroup); + list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) { + list_del(&wh->list); + kfree(wh); + } + kfree(dev_cgroup); +} + +#define DEVCG_ALLOW 1 +#define DEVCG_DENY 2 + +static void set_access(char *acc, short access) +{ + int idx = 0; + memset(acc, 0, 4); + if (access & ACC_READ) + acc[idx++] = 'r'; + if (access & ACC_WRITE) + acc[idx++] = 'w'; + if (access & ACC_MKNOD) + acc[idx++] = 'm'; +} + +static char type_to_char(short type) +{ + if (type == DEV_ALL) + return 'a'; + if (type == DEV_CHAR) + return 'c'; + if (type == DEV_BLOCK) + return 'b'; + return 'X'; +} + +static void set_majmin(char *str, int len, unsigned m) +{ + memset(str, 0, len); + if (m == ~0) + sprintf(str, "*"); + else + snprintf(str, len, "%d", m); +} + +static char *print_whitelist(struct dev_cgroup *devcgroup, int *len) +{ + char *buf, *s, acc[4]; + struct dev_whitelist_item *wh; + int ret; + int count = 0; + char maj[10], min[10]; + + buf = kmalloc(4096, GFP_KERNEL); + if (!buf) + return ERR_PTR(-ENOMEM); + s = buf; + *s = '\0'; + *len = 0; + + spin_lock(&devcgroup->lock); + list_for_each_entry(wh, &devcgroup->whitelist, list) { + set_access(acc, wh->access); + set_majmin(maj, 10, wh->major); + set_majmin(min, 10, wh->minor); + ret = snprintf(s, 4095-(s-buf), "%c %s:%s %s\n", + type_to_char(wh->type), maj, min, acc); + if (s+ret >= buf+4095) { + kfree(buf); + buf = ERR_PTR(-ENOMEM); + break; + } + s += ret; + *len += ret; + count++; + } + spin_unlock(&devcgroup->lock); + + return buf; +} + +static ssize_t devcgroup_access_read(struct cgroup *cgroup, + struct cftype *cft, struct file *file, + char __user *userbuf, size_t nbytes, loff_t *ppos) +{ + struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup); + int filetype = cft->private; + char *buffer; + int uninitialized_var(len); + int retval; + + if (filetype != DEVCG_ALLOW) + return -EINVAL; + buffer = print_whitelist(devcgroup, &len); + if (IS_ERR(buffer)) + return PTR_ERR(buffer); + + retval = simple_read_from_buffer(userbuf, nbytes, ppos, buffer, len); + kfree(buffer); + return retval; +} + +/* + * may_access_whitelist: + * does the access granted to dev_cgroup c contain the access + * requested in whitelist item refwh. + * return 1 if yes, 0 if no. + * call with c->lock held + */ +static int may_access_whitelist(struct dev_cgroup *c, + struct dev_whitelist_item *refwh) +{ + struct dev_whitelist_item *whitem; + + list_for_each_entry(whitem, &c->whitelist, list) { + if (whitem->type & DEV_ALL) + return 1; + if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK)) + continue; + if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR)) + continue; + if (whitem->major != ~0 && whitem->major != refwh->major) + continue; + if (whitem->minor != ~0 && whitem->minor != refwh->minor) + continue; + if (refwh->access & (~(whitem->access | ACC_MASK))) + continue; + return 1; + } + return 0; +} + +/* + * parent_has_perm: + * when adding a new allow rule to a device whitelist, the rule + * must be allowed in the parent device + */ +static int parent_has_perm(struct cgroup *childcg, + struct dev_whitelist_item *wh) +{ + struct cgroup *pcg = childcg->parent; + struct dev_cgroup *parent; + int ret; + + if (!pcg) + return 1; + parent = cgroup_to_devcgroup(pcg); + spin_lock(&parent->lock); + ret = may_access_whitelist(parent, wh); + spin_unlock(&parent->lock); + return ret; +} + +/* + * Modify the whitelist using allow/deny rules. + * CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD + * so we can give a container CAP_MKNOD to let it create devices but not + * modify the whitelist. + * It seems likely we'll want to add a CAP_CONTAINER capability to allow + * us to also grant CAP_SYS_ADMIN to containers without giving away the + * device whitelist controls, but for now we'll stick with CAP_SYS_ADMIN + * + * Taking rules away is always allowed (given CAP_SYS_ADMIN). Granting + * new access is only allowed if you're in the top-level cgroup, or your + * parent cgroup has the access you're asking for. + */ +static ssize_t devcgroup_access_write(struct cgroup *cgroup, struct cftype *cft, + struct file *file, const char __user *userbuf, + size_t nbytes, loff_t *ppos) +{ + struct cgroup *cur_cgroup; + struct dev_cgroup *devcgroup, *cur_devcgroup; + int filetype = cft->private; + char *buffer, *b; + int retval = 0, count; + struct dev_whitelist_item wh; + + if (!capable(CAP_SYS_ADMIN)) + return -EPERM; + + devcgroup = cgroup_to_devcgroup(cgroup); + cur_cgroup = task_cgroup(current, devices_subsys.subsys_id); + cur_devcgroup = cgroup_to_devcgroup(cur_cgroup); + + buffer = kmalloc(nbytes+1, GFP_KERNEL); + if (!buffer) + return -ENOMEM; + + if (copy_from_user(buffer, userbuf, nbytes)) { + retval = -EFAULT; + goto out1; + } + buffer[nbytes] = 0; /* nul-terminate */ + + cgroup_lock(); + if (cgroup_is_removed(cgroup)) { + retval = -ENODEV; + goto out2; + } + + memset(&wh, 0, sizeof(wh)); + b = buffer; + + switch (*b) { + case 'a': + wh.type = DEV_ALL; + wh.access = ACC_MASK; + goto handle; + case 'b': + wh.type = DEV_BLOCK; + break; + case 'c': + wh.type = DEV_CHAR; + break; + default: + retval = -EINVAL; + goto out2; + } + b++; + if (!isspace(*b)) { + retval = -EINVAL; + goto out2; + } + b++; + if (*b == '*') { + wh.major = ~0; + b++; + } else if (isdigit(*b)) { + wh.major = 0; + while (isdigit(*b)) { + wh.major = wh.major*10+(*b-'0'); + b++; + } + } else { + retval = -EINVAL; + goto out2; + } + if (*b != ':') { + retval = -EINVAL; + goto out2; + } + b++; + + /* read minor */ + if (*b == '*') { + wh.minor = ~0; + b++; + } else if (isdigit(*b)) { + wh.minor = 0; + while (isdigit(*b)) { + wh.minor = wh.minor*10+(*b-'0'); + b++; + } + } else { + retval = -EINVAL; + goto out2; + } + if (!isspace(*b)) { + retval = -EINVAL; + goto out2; + } + for (b++, count = 0; count < 3; count++, b++) { + switch (*b) { + case 'r': + wh.access |= ACC_READ; + break; + case 'w': + wh.access |= ACC_WRITE; + break; + case 'm': + wh.access |= ACC_MKNOD; + break; + case '\n': + case '\0': + count = 3; + break; + default: + retval = -EINVAL; + goto out2; + } + } + +handle: + retval = 0; + switch (filetype) { + case DEVCG_ALLOW: + if (!parent_has_perm(cgroup, &wh)) + retval = -EPERM; + else + retval = dev_whitelist_add(devcgroup, &wh); + break; + case DEVCG_DENY: + dev_whitelist_rm(devcgroup, &wh); + break; + default: + retval = -EINVAL; + goto out2; + } + + if (retval == 0) + retval = nbytes; + +out2: + cgroup_unlock(); +out1: + kfree(buffer); + return retval; +} + +static struct cftype dev_cgroup_files[] = { + { + .name = "allow", + .read = devcgroup_access_read, + .write = devcgroup_access_write, + .private = DEVCG_ALLOW, + }, + { + .name = "deny", + .write = devcgroup_access_write, + .private = DEVCG_DENY, + }, +}; + +static int devcgroup_populate(struct cgroup_subsys *ss, + struct cgroup *cgroup) +{ + return cgroup_add_files(cgroup, ss, dev_cgroup_files, + ARRAY_SIZE(dev_cgroup_files)); +} + +struct cgroup_subsys devices_subsys = { + .name = "devices", + .can_attach = devcgroup_can_attach, + .create = devcgroup_create, + .destroy = devcgroup_destroy, + .populate = devcgroup_populate, + .subsys_id = devices_subsys_id, +}; + +int devcgroup_inode_permission(struct inode *inode, int mask) +{ + struct cgroup *cgroup; + struct dev_cgroup *dev_cgroup; + struct dev_whitelist_item *wh; + + dev_t device = inode->i_rdev; + if (!device) + return 0; + if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode)) + return 0; + cgroup = task_cgroup(current, devices_subsys.subsys_id); + dev_cgroup = cgroup_to_devcgroup(cgroup); + if (!dev_cgroup) + return 0; + + spin_lock(&dev_cgroup->lock); + list_for_each_entry(wh, &dev_cgroup->whitelist, list) { + if (wh->type & DEV_ALL) + goto acc_check; + if ((wh->type & DEV_BLOCK) && !S_ISBLK(inode->i_mode)) + continue; + if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode)) + continue; + if (wh->major != ~0 && wh->major != imajor(inode)) + continue; + if (wh->minor != ~0 && wh->minor != iminor(inode)) + continue; +acc_check: + if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE)) + continue; + if ((mask & MAY_READ) && !(wh->access & ACC_READ)) + continue; + spin_unlock(&dev_cgroup->lock); + return 0; + } + spin_unlock(&dev_cgroup->lock); + + return -EPERM; +} + +int devcgroup_inode_mknod(int mode, dev_t dev) +{ + struct cgroup *cgroup; + struct dev_cgroup *dev_cgroup; + struct dev_whitelist_item *wh; + + cgroup = task_cgroup(current, devices_subsys.subsys_id); + dev_cgroup = cgroup_to_devcgroup(cgroup); + if (!dev_cgroup) + return 0; + + spin_lock(&dev_cgroup->lock); + list_for_each_entry(wh, &dev_cgroup->whitelist, list) { + if (wh->type & DEV_ALL) + goto acc_check; + if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode)) + continue; + if ((wh->type & DEV_CHAR) && !S_ISCHR(mode)) + continue; + if (wh->major != ~0 && wh->major != MAJOR(dev)) + continue; + if (wh->minor != ~0 && wh->minor != MINOR(dev)) + continue; +acc_check: + if (!(wh->access & ACC_MKNOD)) + continue; + spin_unlock(&dev_cgroup->lock); + return 0; + } + spin_unlock(&dev_cgroup->lock); + return -EPERM; +} |