On Tue, 12 Apr 2022 12:24:59 -0700 Tadeusz Struk wrote:
Syzbot found a corrupted list bug scenario that can be triggered from
cgroup css_create(). The reproduces writes to cgroup.subtree_control
file, which invokes cgroup_apply_control_enable(), css_create(), and
css_populate_dir(), which then randomly fails with a fault injected -ENOMEM.
In such scenario the css_create() error path rcu enqueues css_free_rwork_fn
work for an css->refcnt initialized with css_release() destructor,
and there is a chance that the css_release() function will be invoked
Could you tip-point the percpu_ref_kill needed to trigger the css_release()?
for a cgroup_subsys_state, for which a destroy_work has already been
queued via css_create() error path. This causes a list_add corruption
as can be seen in the syzkaller report [1].
This can be avoided by adding a check to css_release() that checks
if it has already been enqueued.
[1] https://syzkaller.appspot.com/bug?id=e26e54d6eac9d9fb50b221ec3e4627b327465dbd
Given my failure of finding the lore URL to what was
Reported-by: syzbot+e42ae441c3b10acf9e9d@xxxxxxxxxxxxxxxxxxxxxxxxx
such a link is welcome to see the list corruption.
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Zefan Li <lizefan.x@xxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: Andrii Nakryiko <andrii@xxxxxxxxxx>
Cc: Martin KaFai Lau <kafai@xxxxxx>
Cc: Song Liu <songliubraving@xxxxxx>
Cc: Yonghong Song <yhs@xxxxxx>
Cc: John Fastabend <john.fastabend@xxxxxxxxx>
Cc: KP Singh <kpsingh@xxxxxxxxxx>
Cc: <cgroups@xxxxxxxxxxxxxxx>
Cc: <netdev@xxxxxxxxxxxxxxx>
Cc: <bpf@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Cc: <linux-kernel@xxxxxxxxxxxxxxx>
Reported-by: syzbot+e42ae441c3b10acf9e9d@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 8f36aaec9c92 ("cgroup: Use rcu_work instead of explicit rcu and work item")
Signed-off-by: Tadeusz Struk <tadeusz.struk@xxxxxxxxxx>
---
kernel/cgroup/cgroup.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index adb820e98f24..9ae2de29f8c9 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -5210,8 +5210,11 @@ static void css_release(struct percpu_ref *ref)
struct cgroup_subsys_state *css =
container_of(ref, struct cgroup_subsys_state, refcnt);
- INIT_WORK(&css->destroy_work, css_release_work_fn);
- queue_work(cgroup_destroy_wq, &css->destroy_work);
+ if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT,
+ work_data_bits(&css->destroy_work))) {
+ INIT_WORK(&css->destroy_work, css_release_work_fn);
+ queue_work(cgroup_destroy_wq, &css->destroy_work);
+ }
}
static void init_and_link_css(struct cgroup_subsys_state *css,
--
2.35.1