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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Wed, 2 Mar 2022 20:00:26 -0800
Message-ID: <CAADnVQJvbgq3j5SUb3OCbkndgpqeYNAv4Xgo2gOav0mC2f=vmg@mail.gmail.com>
Subject: Re: [PATCH bpf-next v1 8/9] bpf: Introduce cgroup iter
To:     Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc:     Yonghong Song <yhs@fb.com>, Hao Luo <haoluo@google.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>,
        KP Singh <kpsingh@kernel.org>,
        Shakeel Butt <shakeelb@google.com>,
        Joe Burton <jevburton.kernel@gmail.com>,
        Tejun Heo <tj@kernel.org>, Josh Don <joshdon@google.com>,
        Stanislav Fomichev <sdf@google.com>, bpf <bpf@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Wed, Mar 2, 2022 at 7:03 PM Kumar Kartikeya Dwivedi <memxor@gmail.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.