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

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Date:   Tue, 5 Jan 2021 11:30:45 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Yuri Benditovich <yuri.benditovich@...nix.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        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>, yan@...nix.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [RFC PATCH 3/7] tun: allow use of BPF_PROG_TYPE_SCHED_CLS
 program type

On Tue, Jan 05, 2021 at 02:24:12PM +0200, Yuri Benditovich 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);

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.