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=e26e54d6eac9d9fb50b221ec3e4627b327465db...
Cc: Tejun Heo tj@kernel.org Cc: Zefan Li lizefan.x@bytedance.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Christian Brauner brauner@kernel.org Cc: Alexei Starovoitov ast@kernel.org Cc: Daniel Borkmann daniel@iogearbox.net Cc: Andrii Nakryiko andrii@kernel.org Cc: Martin KaFai Lau kafai@fb.com Cc: Song Liu songliubraving@fb.com Cc: Yonghong Song yhs@fb.com Cc: John Fastabend john.fastabend@gmail.com Cc: KP Singh kpsingh@kernel.org Cc: cgroups@vger.kernel.org Cc: netdev@vger.kernel.org Cc: bpf@vger.kernel.org Cc: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org
Reported-by: syzbot+e42ae441c3b10acf9e9d@syzkaller.appspotmail.com Fixes: 8f36aaec9c92 ("cgroup: Use rcu_work instead of explicit rcu and work item") Signed-off-by: Tadeusz Struk tadeusz.struk@linaro.org --- 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,