| From 07cd12945551b63ecb1a349d50a6d69d1d6feb4a Mon Sep 17 00:00:00 2001 |
| From: Tejun Heo <tj@kernel.org> |
| Date: Thu, 26 Jan 2017 16:47:28 -0500 |
| Subject: [PATCH] cgroup: don't online subsystems before cgroup_name/path() are |
| operational |
| |
| commit 07cd12945551b63ecb1a349d50a6d69d1d6feb4a upstream. |
| |
| While refactoring cgroup creation, a5bca2152036 ("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: a5bca2152036 ("cgroup: factor out cgroup_create() out of cgroup_mkdir()") |
| Cc: stable@vger.kernel.org # v4.6+ |
| |
| diff --git a/kernel/cgroup.c b/kernel/cgroup.c |
| index 2ee9ec3051b2..688dd02af985 100644 |
| --- a/kernel/cgroup.c |
| +++ b/kernel/cgroup.c |
| @@ -5221,6 +5221,11 @@ err_free_css: |
| 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 @@ out_cancel_ref: |
| 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, |
| -- |
| 2.12.0 |
| |