From d1897c9538edafd4ae6bbd03cc075962ddde2c21 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 21 Feb 2018 11:39:22 -0800 Subject: [PATCH] cgroup: fix rule checking for threaded mode switching A domain cgroup isn't allowed to be turned threaded if its subtree is populated or domain controllers are enabled. cgroup_enable_threaded() depended on cgroup_can_be_thread_root() test to enforce this rule. A parent which has populated domain descendants or have domain controllers enabled can't become a thread root, so the above rules are enforced automatically. However, for the root cgroup which can host mixed domain and threaded children, cgroup_can_be_thread_root() doesn't check any of those conditions and thus first level cgroups ends up escaping those rules. This patch fixes the bug by adding explicit checks for those rules in cgroup_enable_threaded(). Reported-by: Michael Kerrisk (man-pages) Signed-off-by: Tejun Heo Fixes: 8cfd8147df67 ("cgroup: implement cgroup v2 thread support") Cc: stable@vger.kernel.org # v4.14+ --- kernel/cgroup/cgroup.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 8cda3bc3ae22..4bfb2908ec15 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -3183,6 +3183,16 @@ static int cgroup_enable_threaded(struct cgroup *cgrp) if (cgroup_is_threaded(cgrp)) return 0; + /* + * If @cgroup is populated or has domain controllers enabled, it + * can't be switched. While the below cgroup_can_be_thread_root() + * test can catch the same conditions, that's only when @parent is + * not mixable, so let's check it explicitly. + */ + if (cgroup_is_populated(cgrp) || + cgrp->subtree_control & ~cgrp_dfl_threaded_ss_mask) + return -EOPNOTSUPP; + /* we're joining the parent's domain, ensure its validity */ if (!cgroup_is_valid_domain(dom_cgrp) || !cgroup_can_be_thread_root(dom_cgrp))