linux-kernel - Re: [PATCH bpf-next v1 8/9] bpf: Introduce cgroup iter

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Date:   Wed, 2 Mar 2022 20:00:26 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc:     Yonghong Song <yhs@...com>, Hao Luo <haoluo@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        KP Singh <kpsingh@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Joe Burton <jevburton.kernel@...il.com>,
        Tejun Heo <tj@...nel.org>, Josh Don <joshdon@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>, bpf <bpf@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v1 8/9] bpf: Introduce cgroup iter

On Wed, Mar 2, 2022 at 7:03 PM Kumar Kartikeya Dwivedi <memxor@...il.com> wrote:
> >
>
> I think current approach is also not safe if cgroup_id gets reused, right? I.e.
> it only does cgroup_get_from_id in seq_start, not at attach time, so it may not
> be the same cgroup when calling read(2). kernfs is using idr_alloc_cyclic, so it
> is less likely to occur, but since it wraps around to find a free ID it might
> not be theoretical.

cgroupid is 64-bit.