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: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Serge 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 236fffa..9da3532 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -41,6 +41,7 @@
short type;
short access;
struct list_head list;
+ struct rcu_head rcu;
};
struct dev_cgroup {
@@ -133,11 +134,19 @@
}
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 @@
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 @@
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 @@
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 @@
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 @@
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 @@
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;
}