From: Nicolas Dichtel <nicolas.dich...@6wind.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 <will...@google.com> > CC: Maxim Mikityanskiy <maxi...@mellanox.com> > Signed-off-by: Nicolas Dichtel <nicolas.dich...@6wind.com> > --- > > v1 -> v2: > reset nh offset only for small packets sent on a variable hard hdr len > device Applied.
