Re: [RFC PATCH 3/7] tun: allow use of BPF_PROG_TYPE_SCHED_CLS program type

From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Yuri Benditovich <yuri.benditovich@daynix.com>
Cc: "David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>,
	yan@daynix.com, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [RFC PATCH 3/7] tun: allow use of BPF_PROG_TYPE_SCHED_CLS program type
Date: Tue, 5 Jan 2021 11:30:45 -0800	[thread overview]
Message-ID: <20210105193045.g3q6n3dsl6idthbe@ast-mbp> (raw)
In-Reply-To: <20210105122416.16492-4-yuri.benditovich@daynix.com>

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@daynix.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.