This is a note to let you know that I've just added the patch titled cgroup: don't online subsystems before cgroup_name/path() are operational to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: cgroup-don-t-online-subsystems-before-cgroup_name-path-are-operational.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 07cd12945551b63ecb1a349d50a6d69d1d6feb4a Mon Sep 17 00:00:00 2001 From: Tejun Heo <tj@xxxxxxxxxx> Date: Thu, 26 Jan 2017 16:47:28 -0500 Subject: cgroup: don't online subsystems before cgroup_name/path() are operational From: Tejun Heo <tj@xxxxxxxxxx> 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@xxxxxxxxxx> Reported-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx> Fixes: a5bca2152036 ("cgroup: factor out cgroup_create() out of cgroup_mkdir()") Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/cgroup.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-) --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -5219,6 +5219,11 @@ 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; @@ -5283,11 +5288,6 @@ static struct cgroup *cgroup_create(stru 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: @@ -5295,9 +5295,6 @@ 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, Patches currently in stable-queue which might be from tj@xxxxxxxxxx are queue-4.9/ata-sata_mv-handle-return-value-of-devm_ioremap.patch queue-4.9/libata-apply-max_sec_1024-to-all-cx1-jb-hp-devices.patch queue-4.9/libata-fix-ata-request-sense.patch queue-4.9/percpu-refcount-fix-reference-leak-during-percpu-atomic-transition.patch queue-4.9/cgroup-don-t-online-subsystems-before-cgroup_name-path-are-operational.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html