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 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 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