cgroup: pids: fix invalid get/put usage
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>
diff --git a/kernel/cgroup_pids.c b/kernel/cgroup_pids.c
index d754888..806cd76 100644
--- a/kernel/cgroup_pids.c
+++ b/kernel/cgroup_pids.c
@@ -173,11 +173,11 @@
struct pids_cgroup *old_pids;
/*
- * Grab a ref to each task's css. We don't drop the ref until
- * we either fail and hit ->cancel_attach() or succeed and hit
- * ->attach().
+ * No need to pin @old_css between here and cancel_attach()
+ * because cgroup core protects it from being freed before
+ * 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);
pids_charge(pids, 1);
@@ -202,19 +202,9 @@
pids_charge(old_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)
{
struct cgroup_subsys_state *css;
@@ -354,7 +344,6 @@
struct cgroup_subsys pids_cgrp_subsys = {
.css_alloc = pids_css_alloc,
.css_free = pids_css_free,
- .attach = pids_attach,
.can_attach = pids_can_attach,
.cancel_attach = pids_cancel_attach,
.can_fork = pids_can_fork,