The l2tp [get|set]sockopt() code has fallen back to the UDP functions
for socket option levels != SOL_PPPOL2TP since day one, but that has
never actually worked, since the l2tp socket isn't an inet socket.

As David Miller points out:

  "If we wanted this to work, it'd have to look up the tunnel and then
   use tunnel->sk, but I wonder how useful that would be"

Since this can never have worked so nobody could possibly have depended
on that functionality, just remove the broken code and return -EINVAL.

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Acked-by: James Chapman <jchapman@katalix.com>
Acked-by: David Miller <davem@davemloft.net>
Cc: Phil Turnbull <phil.turnbull@oracle.com>
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Call common functions to set checksum for UDP tunnel.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Added new L2TP configuration options to allow TX and RX of
zero checksums in IPv6. Default is not to use them.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Define separate fields in the sock structure for configuring disabling
checksums in both TX and RX-- sk_no_check_tx and sk_no_check_rx.
The SO_NO_CHECK socket option only affects sk_no_check_tx. Also,
removed UDP_CSUM_* defines since they are no longer necessary.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

It doesn't seem like an protocols are setting anything other
than the default, and allowing to arbitrarily disable checksums
for a whole protocol seems dangerous. This can be done on a per
socket basis.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

As suggested by several people, rename local_df to ignore_df,
since it means "ignore df bit if it is set".

Cc: Maciej Żenczykowski <maze@google.com>
Cc: Florian Westphal <fw@strlen.de>
Cc: David S. Miller <davem@davemloft.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Validating the UDP checksum is now done in UDP before handing
packets to the encapsulation layer. Note that this also eliminates
the "feature" where L2TP can ignore a non-zero UDP checksum (doing
this was contrary to RFC 1122).

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

This replaces 6 identical code snippets with a call to a new
static inline function.

Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

ip_queue_xmit() assumes the skb it has to transmit is attached to an
inet socket. Commit 31c70d5956fc ("l2tp: keep original skb ownership")
changed l2tp to not change skb ownership and thus broke this assumption.

One fix is to add a new 'struct sock *sk' parameter to ip_queue_xmit(),
so that we do not assume skb->sk points to the socket used by l2tp
tunnel.

Fixes: 31c70d5956fc ("l2tp: keep original skb ownership")
Reported-by: Zhan Jianyu <nasa4836@gmail.com>
Tested-by: Zhan Jianyu <nasa4836@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

When l2tp driver tries to get PMTU for the tunnel destination, it uses
the pointer to struct sock that represents PPPoX socket, while it
should use the pointer that represents UDP socket of the tunnel.

Signed-off-by: Dmitry Petukhov <dmgenp@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>