2008-08-25 02:23:43

by Li Zefan

Subject: [PATCH] devcgroup: fix race against rmdir()

During the use of a dev_cgroup, we should guarantee the corresponding
cgroup won't be deleted (i.e. via rmdir). This can be done through
css_get(&dev_cgroup->css), but here we can just get and use the
dev_cgroup under rcu_read_lock.

And also remove checking NULL dev_cgroup, it won't be NULL since a task
always belongs to a cgroup.

Signed-off-by: Li Zefan <[email protected]>
---
security/device_cgroup.c | 18 +++++++++---------
1 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 7bd296c..46f2397 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -508,12 +508,11 @@ int devcgroup_inode_permission(struct inode *inode, int mask)
return 0;
if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
return 0;
- dev_cgroup = css_to_devcgroup(task_subsys_state(current,
- devices_subsys_id));
- if (!dev_cgroup)
- 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;
@@ -533,6 +532,7 @@ acc_check:
rcu_read_unlock();
return 0;
}
+
rcu_read_unlock();

return -EPERM;
@@ -543,12 +543,10 @@ int devcgroup_inode_mknod(int mode, dev_t dev)
struct dev_cgroup *dev_cgroup;
struct dev_whitelist_item *wh;

- dev_cgroup = css_to_devcgroup(task_subsys_state(current,
- devices_subsys_id));
- if (!dev_cgroup)
- return 0;
-
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;
@@ -566,6 +564,8 @@ acc_check:
rcu_read_unlock();
return 0;
}
+
rcu_read_unlock();
+
return -EPERM;
}
--
1.5.4.rc3

2008-08-25 16:44:50

by Serge E. Hallyn

Subject: Re: [PATCH] devcgroup: fix race against rmdir()

Quoting Li Zefan ([email protected]):
> During the use of a dev_cgroup, we should guarantee the corresponding
> cgroup won't be deleted (i.e. via rmdir). This can be done through
> css_get(&dev_cgroup->css), but here we can just get and use the
> dev_cgroup under rcu_read_lock.
>
> And also remove checking NULL dev_cgroup, it won't be NULL since a task
> always belongs to a cgroup.
>
> Signed-off-by: Li Zefan <[email protected]>

Looks good. Thanks, Li.

Acked-by: Serge Hallyn <[email protected]>

> ---
> security/device_cgroup.c | 18 +++++++++---------
> 1 files changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/security/device_cgroup.c b/security/device_cgroup.c
> index 7bd296c..46f2397 100644
> --- a/security/device_cgroup.c
> +++ b/security/device_cgroup.c
> @@ -508,12 +508,11 @@ int devcgroup_inode_permission(struct inode *inode, int mask)
> return 0;
> if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
> return 0;
> - dev_cgroup = css_to_devcgroup(task_subsys_state(current,
> - devices_subsys_id));
> - if (!dev_cgroup)
> - 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;
> @@ -533,6 +532,7 @@ acc_check:
> rcu_read_unlock();
> return 0;
> }
> +
> rcu_read_unlock();
>
> return -EPERM;
> @@ -543,12 +543,10 @@ int devcgroup_inode_mknod(int mode, dev_t dev)
> struct dev_cgroup *dev_cgroup;
> struct dev_whitelist_item *wh;
>
> - dev_cgroup = css_to_devcgroup(task_subsys_state(current,
> - devices_subsys_id));
> - if (!dev_cgroup)
> - return 0;
> -
> 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;
> @@ -566,6 +564,8 @@ acc_check:
> rcu_read_unlock();
> return 0;
> }
> +
> rcu_read_unlock();
> +
> return -EPERM;
> }
> --
> 1.5.4.rc3