[PATCH 5.2 27/85] cgroup: freezer: fix frozen state inheritance

Greg Kroah-Hartman
2019-09-18T06:25:12Z

From: Roman Gushchin <guro@fb.com>

commit 97a61369830ab085df5aed0ff9256f35b07d425a upstream.

If a new child cgroup is created in the frozen cgroup hierarchy
(one or more of ancestor cgroups is frozen), the CGRP_FREEZE cgroup
flag should be set. Otherwise if a process will be attached to the
child cgroup, it won't become frozen.

The problem can be reproduced with the test_cgfreezer_mkdir test.

This is the output before this patch:
~/test_freezer
ok 1 test_cgfreezer_simple
ok 2 test_cgfreezer_tree
ok 3 test_cgfreezer_forkbomb
Cgroup /sys/fs/cgroup/cg_test_mkdir_A/cg_test_mkdir_B isn't frozen
not ok 4 test_cgfreezer_mkdir
ok 5 test_cgfreezer_rmdir
ok 6 test_cgfreezer_migrate
ok 7 test_cgfreezer_ptrace
ok 8 test_cgfreezer_stopped
ok 9 test_cgfreezer_ptraced
ok 10 test_cgfreezer_vfork

And with this patch:
~/test_freezer
ok 1 test_cgfreezer_simple
ok 2 test_cgfreezer_tree
ok 3 test_cgfreezer_forkbomb
ok 4 test_cgfreezer_mkdir
ok 5 test_cgfreezer_rmdir
ok 6 test_cgfreezer_migrate
ok 7 test_cgfreezer_ptrace
ok 8 test_cgfreezer_stopped
ok 9 test_cgfreezer_ptraced
ok 10 test_cgfreezer_vfork

Reported-by: Mark Crossen <mcrossen@fb.com>
Signed-off-by: Roman Gushchin <guro@fb.com>
Fixes: 76f969e8948d ("cgroup: cgroup v2 freezer")
Cc: Tejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org # v5.2+
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
kernel/cgroup/cgroup.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -5213,8 +5213,16 @@ static struct cgroup *cgroup_create(stru
* if the parent has to be frozen, the child has too.
*/
cgrp->freezer.e_freeze = parent->freezer.e_freeze;
- if (cgrp->freezer.e_freeze)
+ if (cgrp->freezer.e_freeze) {
+ /*
+ * Set the CGRP_FREEZE flag, so when a process will be
+ * attached to the child cgroup, it will become frozen.
+ * At this point the new cgroup is unpopulated, so we can
+ * consider it frozen immediately.
+ */
+ set_bit(CGRP_FREEZE, &cgrp->flags);
set_bit(CGRP_FROZEN, &cgrp->flags);
+ }

spin_lock_irq(&css_set_lock);
for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp)) {