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devcgroup: relax white-list protection down to RCU

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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>
This commit is contained in:
Pavel Emelyanov 2008-07-25 01:47:07 -07:00 committed by Linus Torvalds
parent e885dcde75
commit 4efd1a1b2f
1 changed files with 22 additions and 13 deletions
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35
security/device_cgroup.c
View file

@ -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;
}