From: Waiman Long Date: Wed, 3 Jul 2024 18:52:29 +0000 (-0400) Subject: cgroup: Protect css->cgroup write under css_set_lock X-Git-Tag: v5.10.226~55 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=1434b72a2d1210d9f781700004ce98f5443c1ac8;p=thirdparty%2Fkernel%2Fstable.git cgroup: Protect css->cgroup write under css_set_lock [ Upstream commit 57b56d16800e8961278ecff0dc755d46c4575092 ] The writing of css->cgroup associated with the cgroup root in rebind_subsystems() is currently protected only by cgroup_mutex. However, the reading of css->cgroup in both proc_cpuset_show() and proc_cgroup_show() is protected just by css_set_lock. That makes the readers susceptible to racing problems like data tearing or caching. It is also a problem that can be reported by KCSAN. This can be fixed by using READ_ONCE() and WRITE_ONCE() to access css->cgroup. Alternatively, the writing of css->cgroup can be moved under css_set_lock as well which is done by this patch. Signed-off-by: Waiman Long Signed-off-by: Tejun Heo Signed-off-by: Sasha Levin --- diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 030eaed1f06b0..643d8e178f7b9 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -1773,9 +1773,9 @@ int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask) RCU_INIT_POINTER(scgrp->subsys[ssid], NULL); rcu_assign_pointer(dcgrp->subsys[ssid], css); ss->root = dst_root; - css->cgroup = dcgrp; spin_lock_irq(&css_set_lock); + css->cgroup = dcgrp; WARN_ON(!list_empty(&dcgrp->e_csets[ss->id])); list_for_each_entry_safe(cset, cset_pos, &scgrp->e_csets[ss->id], e_cset_node[ss->id]) {