From: David Woodhouse <dwmw2@infradead.org>
To: Jason Wang <jasowang@redhat.com>, netdev@vger.kernel.org
Cc: "Eugenio Pérez" <eperezma@redhat.com>,
"Willem de Bruijn" <willemb@google.com>
Subject: Re: [PATCH v3 4/5] net: tun: fix tun_xdp_one() for IFF_TUN mode
Date: Fri, 25 Jun 2021 09:51:28 +0100 [thread overview]
Message-ID: <32071ebb3f433b239394e243a6fc8a2bc6d36dcb.camel@infradead.org> (raw)
In-Reply-To: <be6ec48e-ffc7-749b-f775-a34d376f474c@redhat.com>
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On Fri, 2021-06-25 at 15:41 +0800, Jason Wang wrote:
> 在 2021/6/24 下午8:30, David Woodhouse 写道:
> > From: David Woodhouse <dwmw@amazon.co.uk>
> >
> > In tun_get_user(), skb->protocol is either taken from the tun_pi header
> > or inferred from the first byte of the packet in IFF_TUN mode, while
> > eth_type_trans() is called only in the IFF_TAP mode where the payload
> > is expected to be an Ethernet frame.
> >
> > The equivalent code path in tun_xdp_one() was unconditionally using
> > eth_type_trans(), which is the wrong thing to do in IFF_TUN mode and
> > corrupts packets.
> >
> > Pull the logic out to a separate tun_skb_set_protocol() function, and
> > call it from both tun_get_user() and tun_xdp_one().
> >
> > XX: It is not entirely clear to me why it's OK to call eth_type_trans()
> > in some cases without first checking that enough of the Ethernet header
> > is linearly present by calling pskb_may_pull().
>
>
> Looks like a bug.
>
>
> > Such a check was never
> > present in the tun_xdp_one() code path, and commit 96aa1b22bd6bb ("tun:
> > correct header offsets in napi frags mode") deliberately added it *only*
> > for the IFF_NAPI_FRAGS mode.
>
>
> We had already checked this in tun_get_user() before:
>
> if ((tun->flags & TUN_TYPE_MASK) == IFF_TAP) {
> align += NET_IP_ALIGN;
> if (unlikely(len < ETH_HLEN ||
> (gso.hdr_len && tun16_to_cpu(tun,
> gso.hdr_len) < ETH_HLEN)))
> return -EINVAL;
> }
We'd checked skb->len, but that doesn't mean we had a full Ethernet
header *linearly* at skb->data, does it?
For the basic tun_get_user() case I suppose we copy_from_user() into a
single linear skb anyway, even if userspace had fragment it and used
writev(). So we *are* probably safe there?
I'm sure we *can* contrive a proof that it's safe for that case, if we
must. But I think we should *need* that proof, if we're going to bypass
the check. And I wasn't comfortable touching that code without it.
We should also have a fairly good reason... it isn't clear to me *why*
we're bothering to avoid the check. Is it so slow, even in the case
where there's nothing to be done?
For a linear skb, the inline pskb_may_pull() is going to immediately
return true because ETH_HLEN < skb_headlen(skb), isn't it? Why optimise
*that* away?
Willem, was there a reason you made that conditional in the first
place?
If we're going to continue to *not* check on the XDP path, we similarly
need a proof that it can't be fragmented. And also a reason to bother
with the "optimisation", of course.
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next prev parent reply other threads:[~2021-06-25 8:51 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-19 13:33 [PATCH] net: tun: fix tun_xdp_one() for IFF_TUN mode David Woodhouse
2021-06-21 7:00 ` Jason Wang
2021-06-21 10:52 ` David Woodhouse
2021-06-21 14:50 ` David Woodhouse
2021-06-21 20:43 ` David Woodhouse
2021-06-22 4:52 ` Jason Wang
2021-06-22 7:24 ` David Woodhouse
2021-06-22 7:51 ` Jason Wang
2021-06-22 8:10 ` David Woodhouse
2021-06-22 11:36 ` David Woodhouse
2021-06-22 4:34 ` Jason Wang
2021-06-22 4:34 ` Jason Wang
2021-06-22 7:28 ` David Woodhouse
2021-06-22 8:00 ` Jason Wang
2021-06-22 8:29 ` David Woodhouse
2021-06-23 3:39 ` Jason Wang
2021-06-24 12:39 ` David Woodhouse
2021-06-22 16:15 ` [PATCH v2 1/4] " David Woodhouse
2021-06-22 16:15 ` [PATCH v2 2/4] net: tun: don't assume IFF_VNET_HDR in tun_xdp_one() tx path David Woodhouse
2021-06-23 3:46 ` Jason Wang
2021-06-22 16:15 ` [PATCH v2 3/4] vhost_net: validate virtio_net_hdr only if it exists David Woodhouse
2021-06-23 3:48 ` Jason Wang
2021-06-22 16:15 ` [PATCH v2 4/4] vhost_net: Add self test with tun device David Woodhouse
2021-06-23 4:02 ` Jason Wang
2021-06-23 16:12 ` David Woodhouse
2021-06-24 6:12 ` Jason Wang
2021-06-24 10:42 ` David Woodhouse
2021-06-25 2:55 ` Jason Wang
2021-06-25 7:54 ` David Woodhouse
2021-06-23 3:45 ` [PATCH v2 1/4] net: tun: fix tun_xdp_one() for IFF_TUN mode Jason Wang
2021-06-23 8:30 ` David Woodhouse
2021-06-23 13:52 ` David Woodhouse
2021-06-23 17:31 ` David Woodhouse
2021-06-23 22:52 ` David Woodhouse
2021-06-24 6:37 ` Jason Wang
2021-06-24 7:23 ` David Woodhouse
2021-06-24 6:18 ` Jason Wang
2021-06-24 7:05 ` David Woodhouse
2021-06-24 12:30 ` [PATCH v3 1/5] net: add header len parameter to tun_get_socket(), tap_get_socket() David Woodhouse
2021-06-24 12:30 ` [PATCH v3 2/5] net: tun: don't assume IFF_VNET_HDR in tun_xdp_one() tx path David Woodhouse
2021-06-25 6:58 ` Jason Wang
2021-06-24 12:30 ` [PATCH v3 3/5] vhost_net: remove virtio_net_hdr validation, let tun/tap do it themselves David Woodhouse
2021-06-25 7:33 ` Jason Wang
2021-06-25 8:37 ` David Woodhouse
2021-06-28 4:23 ` Jason Wang
2021-06-28 11:23 ` David Woodhouse
2021-06-28 23:29 ` David Woodhouse
2021-06-29 3:43 ` Jason Wang
2021-06-29 6:59 ` David Woodhouse
2021-06-29 10:49 ` David Woodhouse
2021-06-29 13:15 ` David Woodhouse
2021-06-30 4:39 ` Jason Wang
2021-06-30 10:02 ` David Woodhouse
2021-07-01 4:13 ` Jason Wang
2021-07-01 17:39 ` David Woodhouse
2021-07-02 3:13 ` Jason Wang
2021-07-02 8:08 ` David Woodhouse
2021-07-02 8:50 ` Jason Wang
2021-07-09 15:04 ` Eugenio Perez Martin
2021-06-29 3:21 ` Jason Wang
2021-06-24 12:30 ` [PATCH v3 4/5] net: tun: fix tun_xdp_one() for IFF_TUN mode David Woodhouse
2021-06-25 7:41 ` Jason Wang
2021-06-25 8:51 ` David Woodhouse [this message]
2021-06-28 4:27 ` Jason Wang
2021-06-28 10:43 ` David Woodhouse
2021-06-25 18:43 ` Willem de Bruijn
2021-06-25 19:00 ` David Woodhouse
2021-06-24 12:30 ` [PATCH v3 5/5] vhost_net: Add self test with tun device David Woodhouse
2021-06-25 5:00 ` [PATCH v3 1/5] net: add header len parameter to tun_get_socket(), tap_get_socket() Jason Wang
2021-06-25 8:23 ` David Woodhouse
2021-06-28 4:22 ` Jason Wang
2021-06-25 18:13 ` Willem de Bruijn
2021-06-25 18:55 ` David Woodhouse
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