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cgroup: don't online subsystems before cgroup_name/path() are operational

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While refactoring cgroup creation, a5bca21520 ("cgroup: factor out
cgroup_create() out of cgroup_mkdir()") incorrectly onlined subsystems
before the new cgroup is associated with it kernfs_node.  This is fine
for cgroup proper but cgroup_name/path() depend on the associated
kernfs_node and if a subsystem makes the new cgroup_subsys_state
visible, which they're allowed to after onlining, it can lead to NULL
dereference.

The current code performs cgroup creation and subsystem onlining in
cgroup_create() and cgroup_mkdir() makes the cgroup and subsystems
visible afterwards.  There's no reason to online the subsystems early
and we can simply drop cgroup_apply_control_enable() call from
cgroup_create() so that the subsystems are onlined and made visible at
the same time.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Fixes: a5bca21520 ("cgroup: factor out cgroup_create() out of cgroup_mkdir()") 
Cc: stable@vger.kernel.org # v4.6+
This commit is contained in:
Tejun Heo 2017-01-26 16:47:28 -05:00
parent 7ce7d89f48
commit 07cd129455
1 changed files with 5 additions and 8 deletions
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13
kernel/cgroup.c
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@ -5221,6 +5221,11 @@ static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
return ERR_PTR(err);
}
/*
* The returned cgroup is fully initialized including its control mask, but
* it isn't associated with its kernfs_node and doesn't have the control
* mask applied.
*/
static struct cgroup *cgroup_create(struct cgroup *parent)
{
struct cgroup_root *root = parent->root;
@ -5288,11 +5293,6 @@ static struct cgroup *cgroup_create(struct cgroup *parent)
cgroup_propagate_control(cgrp);
/* @cgrp doesn't have dir yet so the following will only create csses */
ret = cgroup_apply_control_enable(cgrp);
if (ret)
goto out_destroy;
return cgrp;
out_cancel_ref:
@ -5300,9 +5300,6 @@ static struct cgroup *cgroup_create(struct cgroup *parent)
out_free_cgrp:
kfree(cgrp);
return ERR_PTR(ret);
out_destroy:
cgroup_destroy_locked(cgrp);
return ERR_PTR(ret);
}
static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,