From: Tejun Heo <tj@kernel.org>
Date: Wed, 27 Nov 2013 23:16:21 +0000 (-0500)
Subject: cgroup: fix cgroup_subsys_state leak for seq_files
X-Git-Tag: submit/tizen/20160422.055611~1^2~99^2~18^2~2470^2~2
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=e605b36575e896edd8161534550c9ea021b03bc0;p=sdk%2Femulator%2Femulator-kernel.git

cgroup: fix cgroup_subsys_state leak for seq_files

If a cgroup file implements either read_map() or read_seq_string(),
such file is served using seq_file by overriding file->f_op to
cgroup_seqfile_operations, which also overrides the release method to
single_release() from cgroup_file_release().

Because cgroup_file_open() didn't use to acquire any resources, this
used to be fine, but since f7d58818ba42 ("cgroup: pin
cgroup_subsys_state when opening a cgroupfs file"), cgroup_file_open()
pins the css (cgroup_subsys_state) which is put by
cgroup_file_release().  The patch forgot to update the release path
for seq_files and each open/release cycle leaks a css reference.

Fix it by updating cgroup_file_release() to also handle seq_files and
using it for seq_file release path too.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org # v3.12
---

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index a7b98ee35ef7..8b729c278b64 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -199,6 +199,7 @@ static void cgroup_destroy_css_killed(struct cgroup *cgrp);
 static int cgroup_destroy_locked(struct cgroup *cgrp);
 static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
 			      bool is_add);
+static int cgroup_file_release(struct inode *inode, struct file *file);
 
 /**
  * cgroup_css - obtain a cgroup's css for the specified subsystem
@@ -2429,7 +2430,7 @@ static const struct file_operations cgroup_seqfile_operations = {
 	.read = seq_read,
 	.write = cgroup_file_write,
 	.llseek = seq_lseek,
-	.release = single_release,
+	.release = cgroup_file_release,
 };
 
 static int cgroup_file_open(struct inode *inode, struct file *file)
@@ -2490,6 +2491,8 @@ static int cgroup_file_release(struct inode *inode, struct file *file)
 		ret = cft->release(inode, file);
 	if (css->ss)
 		css_put(css);
+	if (file->f_op == &cgroup_seqfile_operations)
+		single_release(inode, file);
 	return ret;
 }