linux-kernel - Re: [RFC PATCH 3/7] tun: allow use of BPF_PROG_TYPE_SCHED

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Date:   Tue, 12 Jan 2021 22:40:42 +0200
From:   Yuri Benditovich <yuri.benditovich@...nix.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, rdunlap@...radead.org,
        willemb@...gle.com, gustavoars@...nel.org,
        herbert@...dor.apana.org.au, steffen.klassert@...unet.com,
        pablo@...filter.org, decui@...rosoft.com, cai@....pw,
        jakub@...udflare.com, elver@...gle.com, pabeni@...hat.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        bpf@...r.kernel.org
Cc:     Yan Vugenfirer <yan@...nix.com>
Subject: Re: [RFC PATCH 3/7] tun: allow use of BPF_PROG_TYPE_SCHED_CLS program type

On Tue, Jan 12, 2021 at 9:42 PM Yuri Benditovich
<yuri.benditovich@...nix.com> wrote:
>
> This program type can set skb hash value. It will be useful
> when the tun will support hash reporting feature if virtio-net.
>
> Signed-off-by: Yuri Benditovich <yuri.benditovich@...nix.com>
> ---
>  drivers/net/tun.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 7959b5c2d11f..455f7afc1f36 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -2981,6 +2981,8 @@ static int tun_set_ebpf(struct tun_struct *tun, struct tun_prog __rcu **prog_p,
>                 prog = NULL;
>         } else {
>                 prog = bpf_prog_get_type(fd, BPF_PROG_TYPE_SOCKET_FILTER);
> +               if (IS_ERR(prog))
> +                       prog = bpf_prog_get_type(fd, BPF_PROG_TYPE_SCHED_CLS);
>                 if (IS_ERR(prog))
>                         return PTR_ERR(prog);
>         }

Comment from Alexei Starovoitov:
Patches 1 and 2 are missing for me, so I couldn't review properly,
but this diff looks odd.
It allows sched_cls prog type to attach to tun.
That means everything that sched_cls progs can do will be done from tun hook?
sched_cls assumes l2 and can modify the packet.
I think crashes are inevitable.

> --
> 2.17.1
>