linux-kernel - Re: [PATCH net-next v2] tun: support NAPI for packets received from batched XDP buffs

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Message-ID: <CACGkMEuWLQ6fGXiew_1WGuLYsxEkT+vFequHpZW1KvH=3wcF-w@mail.gmail.com>
Date:   Mon, 28 Feb 2022 13:17:22 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Harold Huang <baymaxhuang@...il.com>,
        netdev <netdev@...r.kernel.org>, Paolo Abeni <pabeni@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:XDP (eXpress Data Path)" <bpf@...r.kernel.org>
Subject: Re: [PATCH net-next v2] tun: support NAPI for packets received from
 batched XDP buffs

On Mon, Feb 28, 2022 at 12:59 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
>
>
> On Sun, Feb 27, 2022 at 8:20 PM Jason Wang <jasowang@...hat.com> wrote:
>>
>> On Mon, Feb 28, 2022 at 12:06 PM Eric Dumazet <eric.dumazet@...il.com> wrote:
>>
>> > How big n can be ?
>> >
>> > BTW I could not find where m->msg_controllen was checked in tun_sendmsg().
>> >
>> > struct tun_msg_ctl *ctl = m->msg_control;
>> >
>> > if (ctl && (ctl->type == TUN_MSG_PTR)) {
>> >
>> >      int n = ctl->num;  // can be set to values in [0..65535]
>> >
>> >      for (i = 0; i < n; i++) {
>> >
>> >          xdp = &((struct xdp_buff *)ctl->ptr)[i];
>> >
>> >
>> > I really do not understand how we prevent malicious user space from
>> > crashing the kernel.
>>
>> It looks to me the only user for this is vhost-net which limits it to
>> 64, userspace can't use sendmsg() directly on tap.
>>
>
> Ah right, thanks for the clarification.
>
> (IMO, either remove the "msg.msg_controllen = sizeof(ctl);" from handle_tx_zerocopy(), or add sanity checks in tun_sendmsg())
>
>

Right, Harold, want to do that?

Thanks