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    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 <lizf@cn.fujitsu.com>
    ---
    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


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