netdev - Re: [PATCH bpf-next v8 1/9] bpf: implement getsockopt and setsockopt hooks

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Date:   Mon, 24 Jun 2019 14:19:50 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin Lau <kafai@...com>
Subject: Re: [PATCH bpf-next v8 1/9] bpf: implement getsockopt and setsockopt hooks

On Mon, Jun 24, 2019 at 1:11 PM Stanislav Fomichev <sdf@...gle.com> wrote:
>
> Implement new BPF_PROG_TYPE_CGROUP_SOCKOPT program type and
> BPF_CGROUP_{G,S}ETSOCKOPT cgroup hooks.
>
> BPF_CGROUP_SETSOCKOPT get a read-only view of the setsockopt arguments.
> BPF_CGROUP_GETSOCKOPT can modify the supplied buffer.
> Both of them reuse existing PTR_TO_PACKET{,_END} infrastructure.
>
> The buffer memory is pre-allocated (because I don't think there is
> a precedent for working with __user memory from bpf). This might be
> slow to do for each {s,g}etsockopt call, that's why I've added
> __cgroup_bpf_prog_array_is_empty that exits early if there is nothing
> attached to a cgroup. Note, however, that there is a race between
> __cgroup_bpf_prog_array_is_empty and BPF_PROG_RUN_ARRAY where cgroup
> program layout might have changed; this should not be a problem
> because in general there is a race between multiple calls to
> {s,g}etsocktop and user adding/removing bpf progs from a cgroup.
>
> The return code of the BPF program is handled as follows:
> * 0: EPERM
> * 1: success, continue with next BPF program in the cgroup chain
>
> v8:
> * use s32 for optlen (Andrii Nakryiko)
>
> v7:
> * return only 0 or 1 (Alexei Starovoitov)
> * always run all progs (Alexei Starovoitov)
> * use optval=0 as kernel bypass in setsockopt (Alexei Starovoitov)
>   (decided to use optval=-1 instead, optval=0 might be a valid input)
> * call getsockopt hook after kernel handlers (Alexei Starovoitov)
>
> v6:
> * rework cgroup chaining; stop as soon as bpf program returns
>   0 or 2; see patch with the documentation for the details
> * drop Andrii's and Martin's Acked-by (not sure they are comfortable
>   with the new state of things)
>
> v5:
> * skip copy_to_user() and put_user() when ret == 0 (Martin Lau)
>
> v4:
> * don't export bpf_sk_fullsock helper (Martin Lau)
> * size != sizeof(__u64) for uapi pointers (Martin Lau)
> * offsetof instead of bpf_ctx_range when checking ctx access (Martin Lau)
>
> v3:
> * typos in BPF_PROG_CGROUP_SOCKOPT_RUN_ARRAY comments (Andrii Nakryiko)
> * reverse christmas tree in BPF_PROG_CGROUP_SOCKOPT_RUN_ARRAY (Andrii
>   Nakryiko)
> * use __bpf_md_ptr instead of __u32 for optval{,_end} (Martin Lau)
> * use BPF_FIELD_SIZEOF() for consistency (Martin Lau)
> * new CG_SOCKOPT_ACCESS macro to wrap repeated parts
>
> v2:
> * moved bpf_sockopt_kern fields around to remove a hole (Martin Lau)
> * aligned bpf_sockopt_kern->buf to 8 bytes (Martin Lau)
> * bpf_prog_array_is_empty instead of bpf_prog_array_length (Martin Lau)
> * added [0,2] return code check to verifier (Martin Lau)
> * dropped unused buf[64] from the stack (Martin Lau)
> * use PTR_TO_SOCKET for bpf_sockopt->sk (Martin Lau)
> * dropped bpf_target_off from ctx rewrites (Martin Lau)
> * use return code for kernel bypass (Martin Lau & Andrii Nakryiko)
>
> Cc: Martin Lau <kafai@...com>
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---

Acked-by: Andrii Nakryiko <andriin@...com>