/*
   * 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>

  #include <linux/seq_file.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 rcu_head rcu;

  };
  
  struct dev_cgroup {
  	struct cgroup_subsys_state css;
  	struct list_head whitelist;
  	spinlock_t lock;
  };

  static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
  {
  	return container_of(s, struct dev_cgroup, css);
  }

  static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
  {

  	return css_to_devcgroup(cgroup_subsys_state(cgroup, devices_subsys_id));

  }

  static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
  {
  	return css_to_devcgroup(task_subsys_state(task, devices_subsys_id));
  }

  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, *walk;

  
  	whcopy = kmalloc(sizeof(*whcopy), GFP_KERNEL);
  	if (!whcopy)
  		return -ENOMEM;
  
  	memcpy(whcopy, wh, sizeof(*whcopy));
  	spin_lock(&dev_cgroup->lock);

  	list_for_each_entry(walk, &dev_cgroup->whitelist, list) {
  		if (walk->type != wh->type)
  			continue;
  		if (walk->major != wh->major)
  			continue;
  		if (walk->minor != wh->minor)
  			continue;
  
  		walk->access |= wh->access;
  		kfree(whcopy);
  		whcopy = NULL;
  	}
  
  	if (whcopy != NULL)

  		list_add_tail_rcu(&whcopy->list, &dev_cgroup->whitelist);

  	spin_unlock(&dev_cgroup->lock);
  	return 0;
  }

  static void whitelist_item_free(struct rcu_head *rcu)
  {
  	struct dev_whitelist_item *item;
  
  	item = container_of(rcu, struct dev_whitelist_item, rcu);
  	kfree(item);
  }

  /*
   * 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_rcu(&walk->list);
  			call_rcu(&walk->rcu, whitelist_item_free);

  		}
  	}
  	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_MASK;

  		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

  #define DEVCG_LIST 3

  #define MAJMINLEN 13

  #define ACCLEN 4

  
  static void set_access(char *acc, short access)
  {
  	int idx = 0;

  	memset(acc, 0, ACCLEN);

  	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, unsigned m)

  {

  	if (m == ~0)

  		strcpy(str, "*");

  	else

  		sprintf(str, "%u", m);

  }

  static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
  				struct seq_file *m)

  {

  	struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);

  	struct dev_whitelist_item *wh;

  	char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];

  	rcu_read_lock();
  	list_for_each_entry_rcu(wh, &devcgroup->whitelist, list) {

  		set_access(acc, wh->access);

  		set_majmin(maj, wh->major);
  		set_majmin(min, wh->minor);
  		seq_printf(m, "%c %s:%s %s
  ", type_to_char(wh->type),
  			   maj, min, acc);

  	}

  	rcu_read_unlock();

  	return 0;

  }
  
  /*
   * 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))

  			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 dev_cgroup *childcg,

  				  struct dev_whitelist_item *wh)
  {

  	struct cgroup *pcg = childcg->css.cgroup->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 int devcgroup_update_access(struct dev_cgroup *devcgroup,
  				   int filetype, const char *buffer)

  {

  	struct dev_cgroup *cur_devcgroup;
  	const char *b;

  	char *endp;

  	int retval = 0, count;
  	struct dev_whitelist_item wh;
  
  	if (!capable(CAP_SYS_ADMIN))
  		return -EPERM;

  	cur_devcgroup = task_devcgroup(current);

  
  	memset(&wh, 0, sizeof(wh));
  	b = buffer;
  
  	switch (*b) {
  	case 'a':
  		wh.type = DEV_ALL;
  		wh.access = ACC_MASK;

  		wh.major = ~0;
  		wh.minor = ~0;

  		goto handle;
  	case 'b':
  		wh.type = DEV_BLOCK;
  		break;
  	case 'c':
  		wh.type = DEV_CHAR;
  		break;
  	default:

  		return -EINVAL;

  	}
  	b++;

  	if (!isspace(*b))
  		return -EINVAL;

  	b++;
  	if (*b == '*') {
  		wh.major = ~0;
  		b++;
  	} else if (isdigit(*b)) {

  		wh.major = simple_strtoul(b, &endp, 10);
  		b = endp;

  	} else {

  		return -EINVAL;

  	}

  	if (*b != ':')
  		return -EINVAL;

  	b++;
  
  	/* read minor */
  	if (*b == '*') {
  		wh.minor = ~0;
  		b++;
  	} else if (isdigit(*b)) {

  		wh.minor = simple_strtoul(b, &endp, 10);
  		b = endp;

  	} else {

  		return -EINVAL;

  	}

  	if (!isspace(*b))
  		return -EINVAL;

  	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 '
  ':
  		case '\0':
  			count = 3;
  			break;
  		default:

  			return -EINVAL;

  		}
  	}
  
  handle:
  	retval = 0;
  	switch (filetype) {
  	case DEVCG_ALLOW:

  		if (!parent_has_perm(devcgroup, &wh))
  			return -EPERM;
  		return dev_whitelist_add(devcgroup, &wh);

  	case DEVCG_DENY:
  		dev_whitelist_rm(devcgroup, &wh);
  		break;
  	default:

  		return -EINVAL;

  	}

  	return 0;
  }

  static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft,
  				  const char *buffer)
  {
  	int retval;
  	if (!cgroup_lock_live_group(cgrp))
  		return -ENODEV;
  	retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp),
  					 cft->private, buffer);

  	cgroup_unlock();

  	return retval;
  }
  
  static struct cftype dev_cgroup_files[] = {
  	{
  		.name = "allow",

  		.write_string  = devcgroup_access_write,

  		.private = DEVCG_ALLOW,
  	},
  	{
  		.name = "deny",

  		.write_string = devcgroup_access_write,

  		.private = DEVCG_DENY,
  	},

  	{
  		.name = "list",
  		.read_seq_string = devcgroup_seq_read,
  		.private = DEVCG_LIST,
  	},

  };
  
  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 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;
  }