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Commit 4efd1a1b authored by Pavel Emelyanov's avatar Pavel Emelyanov Committed by Linus Torvalds
Browse files

devcgroup: relax white-list protection down to RCU 



Currently this list is protected with a simple spinlock, even for reading
from one.  This is OK, but can be better.

Actually I want it to be better very much, since after replacing the
OpenVZ device permissions engine with the cgroup-based one I noticed, that
we set 12 default device permissions for each newly created container (for
/dev/null, full, terminals, ect devices), and people sometimes have up to
20 perms more, so traversing the ~30-40 elements list under a spinlock
doesn't seem very good.

Here's the RCU protection for white-list - dev_whitelist_item-s are added
and removed under the devcg->lock, but are looked up in permissions
checking under the rcu_read_lock.

Signed-off-by: default avatarPavel Emelyanov <xemul@openvz.org>
Acked-by: default avatarSerge Hallyn <serue@us.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e885dcde

security/device_cgroup.c

+22 −13
Original line number Diff line number Diff line
@@ -41,6 +41,7 @@ struct dev_whitelist_item { 
	short type;

	short access;

	struct list_head list;

	struct rcu_head rcu;

};



struct dev_cgroup {
@@ -133,11 +134,19 @@ static int dev_whitelist_add(struct dev_cgroup *dev_cgroup, 
	}



	if (whcopy != NULL)

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

		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
@@ -161,8 +170,8 @@ static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup, 
remove:

		walk->access &= ~wh->access;

		if (!walk->access) {

			list_del(&walk->list);

			kfree(walk);

			list_del_rcu(&walk->list);

			call_rcu(&walk->rcu, whitelist_item_free);

		}

	}

	spin_unlock(&dev_cgroup->lock);
@@ -269,15 +278,15 @@ static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft, 
	struct dev_whitelist_item *wh;

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



	spin_lock(&devcgroup->lock);

	list_for_each_entry(wh, &devcgroup->whitelist, list) {

	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\n", type_to_char(wh->type),

			   maj, min, acc);

	}

	spin_unlock(&devcgroup->lock);

	rcu_read_unlock();



	return 0;

}
@@ -510,8 +519,8 @@ int devcgroup_inode_permission(struct inode *inode, int mask) 
	if (!dev_cgroup)

		return 0;



	spin_lock(&dev_cgroup->lock);

	list_for_each_entry(wh, &dev_cgroup->whitelist, list) {

	rcu_read_lock();

	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))
@@ -527,10 +536,10 @@ int devcgroup_inode_permission(struct inode *inode, int mask) 
			continue;

		if ((mask & MAY_READ) && !(wh->access & ACC_READ))

			continue;

		spin_unlock(&dev_cgroup->lock);

		rcu_read_unlock();

		return 0;

	}

	spin_unlock(&dev_cgroup->lock);

	rcu_read_unlock();



	return -EPERM;

}
@@ -545,7 +554,7 @@ int devcgroup_inode_mknod(int mode, dev_t dev) 
	if (!dev_cgroup)

		return 0;



	spin_lock(&dev_cgroup->lock);

	rcu_read_lock();

	list_for_each_entry(wh, &dev_cgroup->whitelist, list) {

		if (wh->type & DEV_ALL)

			goto acc_check;
@@ -560,9 +569,9 @@ int devcgroup_inode_mknod(int mode, dev_t dev) 
acc_check:

		if (!(wh->access & ACC_MKNOD))

			continue;

		spin_unlock(&dev_cgroup->lock);

		rcu_read_unlock();

		return 0;

	}

	spin_unlock(&dev_cgroup->lock);

	rcu_read_unlock();

	return -EPERM;

}