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cgroup: fail if monitored file and event_control are in different cgroup 

If we pass fd of memory.usage_in_bytes of cgroup A to cgroup.event_control
of cgroup B, then we won't get memory usage notification from A but B!

What's worse, if A and B are in different mount hierarchy, we'll end up
accessing NULL pointer!

Disallow this kind of invalid usage.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Acked-by: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Li Zefan 2013-02-18 14:13:35 +08:00 committed by Tejun Heo
parent 810cbee4fa
commit f169007b27
1 changed files with 11 additions and 0 deletions
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11
kernel/cgroup.c
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@ -3856,6 +3856,7 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
const char *buffer)
{
struct cgroup_event *event = NULL;
struct cgroup *cgrp_cfile;
unsigned int efd, cfd;
struct file *efile = NULL;
struct file *cfile = NULL;
@ -3911,6 +3912,16 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
goto fail;
}
/*
* The file to be monitored must be in the same cgroup as
* cgroup.event_control is.
*/
cgrp_cfile = __d_cgrp(cfile->f_dentry->d_parent);
if (cgrp_cfile != cgrp) {
ret = -EINVAL;
goto fail;
}
if (!event->cft->register_event || !event->cft->unregister_event) {
ret = -EINVAL;
goto fail;