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 fixed by separating the css_release and ref_kill paths to work with two separate work_structs.
[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-and-tested-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 --- v2: Add a separate work_struct for the css_ref_kill path instead of checking if a work has already been enqueued. --- include/linux/cgroup-defs.h | 5 +++-- kernel/cgroup/cgroup.c | 14 +++++++------- 2 files changed, 10 insertions(+), 9 deletions(-)
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h index 1bfcfb1af352..92b0c5e8c472 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -178,8 +178,9 @@ struct cgroup_subsys_state { */ atomic_t online_cnt;
- /* percpu_ref killing and RCU release */ - struct work_struct destroy_work; + /* percpu_ref killing, css release, and RCU release work structs */ + struct work_struct release_work; + struct work_struct killed_ref_work; struct rcu_work destroy_rwork;
/* diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index adb820e98f24..3e00a793e15d 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -5099,7 +5099,7 @@ static struct cftype cgroup_base_files[] = { * css_free_work_fn(). * * It is actually hairier because both step 2 and 4 require process context - * and thus involve punting to css->destroy_work adding two additional + * and thus involve punting to css->release_work adding two additional * steps to the already complex sequence. */ static void css_free_rwork_fn(struct work_struct *work) @@ -5154,7 +5154,7 @@ static void css_free_rwork_fn(struct work_struct *work) static void css_release_work_fn(struct work_struct *work) { struct cgroup_subsys_state *css = - container_of(work, struct cgroup_subsys_state, destroy_work); + container_of(work, struct cgroup_subsys_state, release_work); struct cgroup_subsys *ss = css->ss; struct cgroup *cgrp = css->cgroup;
@@ -5210,8 +5210,8 @@ 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); + INIT_WORK(&css->release_work, css_release_work_fn); + queue_work(cgroup_destroy_wq, &css->release_work); }
static void init_and_link_css(struct cgroup_subsys_state *css, @@ -5546,7 +5546,7 @@ int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode) static void css_killed_work_fn(struct work_struct *work) { struct cgroup_subsys_state *css = - container_of(work, struct cgroup_subsys_state, destroy_work); + container_of(work, struct cgroup_subsys_state, killed_ref_work);
mutex_lock(&cgroup_mutex);
@@ -5567,8 +5567,8 @@ static void css_killed_ref_fn(struct percpu_ref *ref) container_of(ref, struct cgroup_subsys_state, refcnt);
if (atomic_dec_and_test(&css->online_cnt)) { - INIT_WORK(&css->destroy_work, css_killed_work_fn); - queue_work(cgroup_destroy_wq, &css->destroy_work); + INIT_WORK(&css->killed_ref_work, css_killed_work_fn); + queue_work(cgroup_destroy_wq, &css->killed_ref_work); } }