linux-kernel - [ 16/22] cgroup: fail if monitored file and event

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Message-Id: <20130929191159.989285833@linuxfoundation.org>
Date:	Sun, 29 Sep 2013 12:27:02 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Li Zefan <lizefan@...wei.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Tejun Heo <tj@...nel.org>,
	Weng Meiling <wengmeiling.weng@...wei.com>
Subject: [ 16/22] cgroup: fail if monitored file and event_control are in different cgroup

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Li Zefan <lizefan@...wei.com>

commit f169007b2773f285e098cb84c74aac0154d65ff7 upstream.

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@...wei.com>
Acked-by: Kirill A. Shutemov <kirill@...temov.name>
Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: Weng Meiling <wengmeiling.weng@...wei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/cgroup.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3476,6 +3476,7 @@ static int cgroup_write_event_control(st
 				      const char *buffer)
 {
 	struct cgroup_event *event = NULL;
+	struct cgroup *cgrp_cfile;
 	unsigned int efd, cfd;
 	struct file *efile = NULL;
 	struct file *cfile = NULL;
@@ -3531,6 +3532,16 @@ static int cgroup_write_event_control(st
 		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;


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