566 lines
12 KiB
C
566 lines
12 KiB
C
/*
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* dev_cgroup.c - device cgroup subsystem
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*
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* Copyright 2007 IBM Corp
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*/
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#include <linux/device_cgroup.h>
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#include <linux/cgroup.h>
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#include <linux/ctype.h>
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#include <linux/list.h>
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#include <linux/uaccess.h>
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#include <linux/seq_file.h>
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#define ACC_MKNOD 1
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#define ACC_READ 2
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#define ACC_WRITE 4
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#define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)
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#define DEV_BLOCK 1
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#define DEV_CHAR 2
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#define DEV_ALL 4 /* this represents all devices */
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/*
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* whitelist locking rules:
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* cgroup_lock() cannot be taken under dev_cgroup->lock.
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* dev_cgroup->lock can be taken with or without cgroup_lock().
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*
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* modifications always require cgroup_lock
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* modifications to a list which is visible require the
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* dev_cgroup->lock *and* cgroup_lock()
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* walking the list requires dev_cgroup->lock or cgroup_lock().
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*
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* reasoning: dev_whitelist_copy() needs to kmalloc, so needs
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* a mutex, which the cgroup_lock() is. Since modifying
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* a visible list requires both locks, either lock can be
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* taken for walking the list.
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*/
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struct dev_whitelist_item {
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u32 major, minor;
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short type;
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short access;
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struct list_head list;
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struct rcu_head rcu;
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};
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struct dev_cgroup {
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struct cgroup_subsys_state css;
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struct list_head whitelist;
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spinlock_t lock;
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};
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static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
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{
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return container_of(s, struct dev_cgroup, css);
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}
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static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
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{
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return css_to_devcgroup(cgroup_subsys_state(cgroup, devices_subsys_id));
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}
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static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
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{
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return css_to_devcgroup(task_subsys_state(task, devices_subsys_id));
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}
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struct cgroup_subsys devices_subsys;
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static int devcgroup_can_attach(struct cgroup_subsys *ss,
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struct cgroup *new_cgroup, struct task_struct *task)
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{
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if (current != task && !capable(CAP_SYS_ADMIN))
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return -EPERM;
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return 0;
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}
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/*
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* called under cgroup_lock()
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*/
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static int dev_whitelist_copy(struct list_head *dest, struct list_head *orig)
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{
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struct dev_whitelist_item *wh, *tmp, *new;
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list_for_each_entry(wh, orig, list) {
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new = kmemdup(wh, sizeof(*wh), GFP_KERNEL);
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if (!new)
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goto free_and_exit;
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list_add_tail(&new->list, dest);
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}
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return 0;
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free_and_exit:
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list_for_each_entry_safe(wh, tmp, dest, list) {
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list_del(&wh->list);
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kfree(wh);
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}
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return -ENOMEM;
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}
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/* Stupid prototype - don't bother combining existing entries */
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/*
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* called under cgroup_lock()
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* since the list is visible to other tasks, we need the spinlock also
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*/
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static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
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struct dev_whitelist_item *wh)
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{
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struct dev_whitelist_item *whcopy, *walk;
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whcopy = kmemdup(wh, sizeof(*wh), GFP_KERNEL);
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if (!whcopy)
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return -ENOMEM;
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spin_lock(&dev_cgroup->lock);
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list_for_each_entry(walk, &dev_cgroup->whitelist, list) {
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if (walk->type != wh->type)
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continue;
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if (walk->major != wh->major)
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continue;
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if (walk->minor != wh->minor)
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continue;
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walk->access |= wh->access;
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kfree(whcopy);
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whcopy = NULL;
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}
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if (whcopy != NULL)
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list_add_tail_rcu(&whcopy->list, &dev_cgroup->whitelist);
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spin_unlock(&dev_cgroup->lock);
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return 0;
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}
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static void whitelist_item_free(struct rcu_head *rcu)
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{
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struct dev_whitelist_item *item;
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item = container_of(rcu, struct dev_whitelist_item, rcu);
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kfree(item);
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}
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/*
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* called under cgroup_lock()
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* since the list is visible to other tasks, we need the spinlock also
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*/
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static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup,
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struct dev_whitelist_item *wh)
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{
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struct dev_whitelist_item *walk, *tmp;
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spin_lock(&dev_cgroup->lock);
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list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) {
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if (walk->type == DEV_ALL)
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goto remove;
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if (walk->type != wh->type)
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continue;
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if (walk->major != ~0 && walk->major != wh->major)
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continue;
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if (walk->minor != ~0 && walk->minor != wh->minor)
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continue;
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remove:
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walk->access &= ~wh->access;
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if (!walk->access) {
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list_del_rcu(&walk->list);
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call_rcu(&walk->rcu, whitelist_item_free);
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}
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}
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spin_unlock(&dev_cgroup->lock);
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}
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/*
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* called from kernel/cgroup.c with cgroup_lock() held.
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*/
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static struct cgroup_subsys_state *devcgroup_create(struct cgroup_subsys *ss,
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struct cgroup *cgroup)
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{
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struct dev_cgroup *dev_cgroup, *parent_dev_cgroup;
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struct cgroup *parent_cgroup;
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int ret;
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dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
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if (!dev_cgroup)
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return ERR_PTR(-ENOMEM);
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INIT_LIST_HEAD(&dev_cgroup->whitelist);
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parent_cgroup = cgroup->parent;
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if (parent_cgroup == NULL) {
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struct dev_whitelist_item *wh;
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wh = kmalloc(sizeof(*wh), GFP_KERNEL);
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if (!wh) {
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kfree(dev_cgroup);
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return ERR_PTR(-ENOMEM);
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}
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wh->minor = wh->major = ~0;
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wh->type = DEV_ALL;
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wh->access = ACC_MASK;
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list_add(&wh->list, &dev_cgroup->whitelist);
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} else {
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parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
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ret = dev_whitelist_copy(&dev_cgroup->whitelist,
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&parent_dev_cgroup->whitelist);
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if (ret) {
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kfree(dev_cgroup);
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return ERR_PTR(ret);
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}
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}
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spin_lock_init(&dev_cgroup->lock);
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return &dev_cgroup->css;
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}
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static void devcgroup_destroy(struct cgroup_subsys *ss,
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struct cgroup *cgroup)
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{
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struct dev_cgroup *dev_cgroup;
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struct dev_whitelist_item *wh, *tmp;
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dev_cgroup = cgroup_to_devcgroup(cgroup);
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list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) {
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list_del(&wh->list);
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kfree(wh);
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}
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kfree(dev_cgroup);
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}
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#define DEVCG_ALLOW 1
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#define DEVCG_DENY 2
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#define DEVCG_LIST 3
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#define MAJMINLEN 13
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#define ACCLEN 4
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static void set_access(char *acc, short access)
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{
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int idx = 0;
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memset(acc, 0, ACCLEN);
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if (access & ACC_READ)
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acc[idx++] = 'r';
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if (access & ACC_WRITE)
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acc[idx++] = 'w';
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if (access & ACC_MKNOD)
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acc[idx++] = 'm';
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}
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static char type_to_char(short type)
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{
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if (type == DEV_ALL)
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return 'a';
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if (type == DEV_CHAR)
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return 'c';
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if (type == DEV_BLOCK)
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return 'b';
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return 'X';
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}
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static void set_majmin(char *str, unsigned m)
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{
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if (m == ~0)
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strcpy(str, "*");
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else
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sprintf(str, "%u", m);
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}
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static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
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struct seq_file *m)
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{
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struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
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struct dev_whitelist_item *wh;
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char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
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rcu_read_lock();
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list_for_each_entry_rcu(wh, &devcgroup->whitelist, list) {
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set_access(acc, wh->access);
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set_majmin(maj, wh->major);
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set_majmin(min, wh->minor);
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seq_printf(m, "%c %s:%s %s\n", type_to_char(wh->type),
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maj, min, acc);
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}
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rcu_read_unlock();
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return 0;
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}
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/*
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* may_access_whitelist:
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* does the access granted to dev_cgroup c contain the access
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* requested in whitelist item refwh.
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* return 1 if yes, 0 if no.
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* call with c->lock held
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*/
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static int may_access_whitelist(struct dev_cgroup *c,
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struct dev_whitelist_item *refwh)
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{
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struct dev_whitelist_item *whitem;
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list_for_each_entry(whitem, &c->whitelist, list) {
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if (whitem->type & DEV_ALL)
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return 1;
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if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK))
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continue;
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if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR))
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continue;
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if (whitem->major != ~0 && whitem->major != refwh->major)
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continue;
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if (whitem->minor != ~0 && whitem->minor != refwh->minor)
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continue;
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if (refwh->access & (~whitem->access))
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continue;
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return 1;
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}
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return 0;
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}
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/*
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* parent_has_perm:
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* when adding a new allow rule to a device whitelist, the rule
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* must be allowed in the parent device
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*/
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static int parent_has_perm(struct dev_cgroup *childcg,
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struct dev_whitelist_item *wh)
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{
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struct cgroup *pcg = childcg->css.cgroup->parent;
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struct dev_cgroup *parent;
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int ret;
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if (!pcg)
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return 1;
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parent = cgroup_to_devcgroup(pcg);
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spin_lock(&parent->lock);
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ret = may_access_whitelist(parent, wh);
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spin_unlock(&parent->lock);
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return ret;
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}
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/*
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* Modify the whitelist using allow/deny rules.
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* CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD
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* so we can give a container CAP_MKNOD to let it create devices but not
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* modify the whitelist.
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* It seems likely we'll want to add a CAP_CONTAINER capability to allow
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* us to also grant CAP_SYS_ADMIN to containers without giving away the
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* device whitelist controls, but for now we'll stick with CAP_SYS_ADMIN
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*
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* Taking rules away is always allowed (given CAP_SYS_ADMIN). Granting
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* new access is only allowed if you're in the top-level cgroup, or your
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* parent cgroup has the access you're asking for.
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*/
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static int devcgroup_update_access(struct dev_cgroup *devcgroup,
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int filetype, const char *buffer)
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{
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struct dev_cgroup *cur_devcgroup;
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const char *b;
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char *endp;
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int count;
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struct dev_whitelist_item wh;
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if (!capable(CAP_SYS_ADMIN))
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return -EPERM;
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cur_devcgroup = task_devcgroup(current);
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memset(&wh, 0, sizeof(wh));
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b = buffer;
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switch (*b) {
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case 'a':
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wh.type = DEV_ALL;
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wh.access = ACC_MASK;
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wh.major = ~0;
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wh.minor = ~0;
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goto handle;
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case 'b':
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wh.type = DEV_BLOCK;
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break;
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case 'c':
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wh.type = DEV_CHAR;
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break;
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default:
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return -EINVAL;
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}
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b++;
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if (!isspace(*b))
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return -EINVAL;
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b++;
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if (*b == '*') {
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wh.major = ~0;
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b++;
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} else if (isdigit(*b)) {
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wh.major = simple_strtoul(b, &endp, 10);
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b = endp;
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} else {
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return -EINVAL;
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}
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if (*b != ':')
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return -EINVAL;
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b++;
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/* read minor */
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if (*b == '*') {
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wh.minor = ~0;
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b++;
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} else if (isdigit(*b)) {
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wh.minor = simple_strtoul(b, &endp, 10);
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b = endp;
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} else {
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return -EINVAL;
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}
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if (!isspace(*b))
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return -EINVAL;
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for (b++, count = 0; count < 3; count++, b++) {
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switch (*b) {
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case 'r':
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wh.access |= ACC_READ;
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break;
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case 'w':
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wh.access |= ACC_WRITE;
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break;
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case 'm':
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wh.access |= ACC_MKNOD;
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break;
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case '\n':
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case '\0':
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count = 3;
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break;
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default:
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return -EINVAL;
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}
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}
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|
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handle:
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switch (filetype) {
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case DEVCG_ALLOW:
|
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if (!parent_has_perm(devcgroup, &wh))
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return -EPERM;
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return dev_whitelist_add(devcgroup, &wh);
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case DEVCG_DENY:
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dev_whitelist_rm(devcgroup, &wh);
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break;
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default:
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return -EINVAL;
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}
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return 0;
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}
|
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|
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static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft,
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const char *buffer)
|
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{
|
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int retval;
|
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if (!cgroup_lock_live_group(cgrp))
|
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return -ENODEV;
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retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp),
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cft->private, buffer);
|
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cgroup_unlock();
|
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return retval;
|
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}
|
|
|
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static struct cftype dev_cgroup_files[] = {
|
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{
|
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.name = "allow",
|
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.write_string = devcgroup_access_write,
|
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.private = DEVCG_ALLOW,
|
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},
|
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{
|
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.name = "deny",
|
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.write_string = devcgroup_access_write,
|
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.private = DEVCG_DENY,
|
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},
|
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{
|
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.name = "list",
|
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.read_seq_string = devcgroup_seq_read,
|
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.private = DEVCG_LIST,
|
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},
|
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};
|
|
|
|
static int devcgroup_populate(struct cgroup_subsys *ss,
|
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struct cgroup *cgroup)
|
|
{
|
|
return cgroup_add_files(cgroup, ss, dev_cgroup_files,
|
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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 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;
|
|
|
|
rcu_read_lock();
|
|
|
|
dev_cgroup = task_devcgroup(current);
|
|
|
|
list_for_each_entry_rcu(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;
|
|
rcu_read_unlock();
|
|
return 0;
|
|
}
|
|
|
|
rcu_read_unlock();
|
|
|
|
return -EPERM;
|
|
}
|
|
|
|
int devcgroup_inode_mknod(int mode, dev_t dev)
|
|
{
|
|
struct dev_cgroup *dev_cgroup;
|
|
struct dev_whitelist_item *wh;
|
|
|
|
rcu_read_lock();
|
|
|
|
dev_cgroup = task_devcgroup(current);
|
|
|
|
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;
|
|
rcu_read_unlock();
|
|
return 0;
|
|
}
|
|
|
|
rcu_read_unlock();
|
|
|
|
return -EPERM;
|
|
}
|