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cgroup: pids: fix invalid get/put usage

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Fix incorrect usage of css_get and css_put to put a different css in
pids_{cancel_,}attach() than the one grabbed in pids_can_attach(). This
could lead to quite serious memory leakage (and unsafe operations on the
putted css).

tj: minor comment update

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Aleksa Sarai 2015-08-25 12:50:44 +10:00 committed by Tejun Heo
parent cf780b7dc7
commit ce52399520
1 changed files with 4 additions and 15 deletions
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19
kernel/cgroup_pids.c
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@ -173,11 +173,11 @@ static int pids_can_attach(struct cgroup_subsys_state *css,
struct pids_cgroup *old_pids; struct pids_cgroup *old_pids;
/* /*
* Grab a ref to each task's css. We don't drop the ref until * No need to pin @old_css between here and cancel_attach()
* we either fail and hit ->cancel_attach() or succeed and hit * because cgroup core protects it from being freed before
* ->attach(). * the migration completes or fails.
*/ */
old_css = task_get_css(task, pids_cgrp_id); old_css = task_css(task, pids_cgrp_id);
old_pids = css_pids(old_css); old_pids = css_pids(old_css);
pids_charge(pids, 1); pids_charge(pids, 1);
@ -202,19 +202,9 @@ static void pids_cancel_attach(struct cgroup_subsys_state *css,
pids_charge(old_pids, 1); pids_charge(old_pids, 1);
pids_uncharge(pids, 1); pids_uncharge(pids, 1);
css_put(old_css);
} }
} }
static void pids_attach(struct cgroup_subsys_state *css,
struct cgroup_taskset *tset)
{
struct task_struct *task;
cgroup_taskset_for_each(task, tset)
css_put(task_css(task, pids_cgrp_id));
}
static int pids_can_fork(struct task_struct *task, void **priv_p) static int pids_can_fork(struct task_struct *task, void **priv_p)
{ {
struct cgroup_subsys_state *css; struct cgroup_subsys_state *css;
@ -354,7 +344,6 @@ static struct cftype pids_files[] = {
struct cgroup_subsys pids_cgrp_subsys = { struct cgroup_subsys pids_cgrp_subsys = {
.css_alloc = pids_css_alloc, .css_alloc = pids_css_alloc,
.css_free = pids_css_free, .css_free = pids_css_free,
.attach = pids_attach,
.can_attach = pids_can_attach, .can_attach = pids_can_attach,
.cancel_attach = pids_cancel_attach, .cancel_attach = pids_cancel_attach,
.can_fork = pids_can_fork, .can_fork = pids_can_fork,