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cgroup: fix cgroup_subsys_state leak for seq_files

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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 f7d58818ba ("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
This commit is contained in:
Tejun Heo 2013-11-27 18:16:21 -05:00
commit e605b36575
1 changed files with 4 additions and 1 deletions
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5
kernel/cgroup.c
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@ -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;
}