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

[Jason Wang]

On Mon, Feb 28, 2022 at 12:59 PM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
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>
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> On Sun, Feb 27, 2022 at 8:20 PM Jason Wang <jasowang@xxxxxxxxxx> wrote:
>>
>> On Mon, Feb 28, 2022 at 12:06 PM Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
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>> > 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())
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>

Right, Harold, want to do that?

Thanks