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cgroup: Protect css->cgroup write under css_set_lock

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[ Upstream commit 57b56d1680 ]

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 <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Waiman Long
2024-07-03 14:52:29 -04:00
committed by Greg Kroah-Hartman
parent 70e66ea0be
commit 3cff144cb3
1 changed files with 1 additions and 1 deletions
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kernel/cgroup/cgroup.c
+1 -1
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@@ -1852,9 +1852,9 @@ 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]) {