netdev - Re: [PATCH net v2] af_packet: fix raw sockets over 6in4 tunnel

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Message-ID: <CAF=yD-+M=FG+a1ykO5ucBSfE0vvV3C_cNBUH1p55Cy1e7mHA-g@mail.gmail.com>
Date:   Wed, 20 Feb 2019 13:39:23 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Sasha Levin <sashal@...nel.org>
Cc:     David Miller <davem@...emloft.net>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Network Development <netdev@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Maxim Mikityanskiy <maximmi@...lanox.com>
Subject: Re: [PATCH net v2] af_packet: fix raw sockets over 6in4 tunnel

On Mon, Feb 18, 2019 at 1:50 PM Sasha Levin <sashal@...nel.org> wrote:
>
> On Thu, Jan 17, 2019 at 03:55:27PM -0800, David Miller wrote:
> >From: Nicolas Dichtel <nicolas.dichtel@...nd.com>
> >Date: Thu, 17 Jan 2019 11:27:22 +0100
> >
> >> Since commit cb9f1b783850, scapy (which uses an AF_PACKET socket in
> >> SOCK_RAW mode) is unable to send a basic icmp packet over a sit tunnel:
> >>
> >> Here is a example of the setup:
> >> $ ip link set ntfp2 up
> >> $ ip addr add 10.125.0.1/24 dev ntfp2
> >> $ ip tunnel add tun1 mode sit ttl 64 local 10.125.0.1 remote 10.125.0.2 dev ntfp2
> >> $ ip addr add fd00:cafe:cafe::1/128 dev tun1
> >> $ ip link set dev tun1 up
> >> $ ip route add fd00:200::/64 dev tun1
> >> $ scapy
> >>>>> p = []
> >>>>> p += IPv6(src='fd00:100::1', dst='fd00:200::1')/ICMPv6EchoRequest()
> >>>>> send(p, count=1, inter=0.1)
> >>>>> quit()
> >> $ ip -s link ls dev tun1 | grep -A1 "TX.*errors"
> >>     TX: bytes  packets  errors  dropped carrier collsns
> >>     0          0        1       0       0       0
> >>
> >> The problem is that the network offset is set to the hard_header_len of the
> >> output device (tun1, ie 14 + 20) and in our case, because the packet is
> >> small (48 bytes) the pskb_inet_may_pull() fails (it tries to pull 40 bytes
> >> (ipv6 header) starting from the network offset).
> >>
> >> This problem is more generally related to device with variable hard header
> >> length. To avoid a too intrusive patch in the current release, a (ugly)
> >> workaround is proposed in this patch. It has to be cleaned up in net-next.
> >>
> >> Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=993675a3100b1
> >> Link: http://patchwork.ozlabs.org/patch/1024489/
> >> Fixes: cb9f1b783850 ("ip: validate header length on virtual device xmit")
> >> CC: Willem de Bruijn <willemb@...gle.com>
> >> CC: Maxim Mikityanskiy <maximmi@...lanox.com>
> >> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
> >> ---
> >>
> >> v1 -> v2:
> >>   reset nh offset only for small packets sent on a variable hard hdr len device
> >
> >Applied.
>
> Should this go to -stable as well? The patch it fixes is in 4.20.

I believe so. It was also backported to 4.19 stable.