Re: [PATCH bpf-next v2 2/6] bpf: Introduce css_task open-coded iterator kfuncs

Martin KaFai Lau
2023-09-12T19:57:57Z

On 9/12/23 12:01 AM, Chuyi Zhou wrote:
> +__bpf_kfunc int bpf_iter_css_task_new(struct bpf_iter_css_task *it,
> + struct cgroup_subsys_state *css, unsigned int flags)
> +{
> + struct bpf_iter_css_task_kern *kit = (void *)it;
> +
> + BUILD_BUG_ON(sizeof(struct bpf_iter_css_task_kern) != sizeof(struct bpf_iter_css_task));
> + BUILD_BUG_ON(__alignof__(struct bpf_iter_css_task_kern) !=
> + __alignof__(struct bpf_iter_css_task));
> +
> + switch (flags) {
> + case CSS_TASK_ITER_PROCS | CSS_TASK_ITER_THREADED:
> + case CSS_TASK_ITER_PROCS:
> + case 0:
> + break;
> + default:
> + return -EINVAL;
> + }
> +
> + kit->css_it = kzalloc(sizeof(struct css_task_iter), GFP_KERNEL);
> + if (!kit->css_it)
> + return -ENOMEM;
> + css_task_iter_start(css, flags, kit->css_it);
> + return 0;
> +}
> +

> +static bool check_css_task_iter_allowlist(struct bpf_verifier_env *env)
> +{
> + enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
> +
> + switch (prog_type) {
> + case BPF_PROG_TYPE_LSM:

This will allow the non-sleepable lsm prog to call bpf_iter_css_task_new. The
above kzalloc(GFP_KERNEL) in bpf_iter_css_task_new should trigger a lockdep
error in the lsm selftest in patch 6.

> + return true;
> + case BPF_TRACE_ITER:
> + return env->prog->aux->sleepable;
> + default:
> + return false;
> + }
> +}