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David S. Miller 2e40b823f0 Merge branch 'l2tp-remove-configurable-offset-parameters'
James Chapman says:

====================
l2tp: remove configurable offset parameters

This patch series removes all code to support a configurable offset in
transmitted l2tp packets. Code to handle this is incomplete and buggy
and has been this way for years. If anyone tried to configure an
offset, it would be ignored for L2TPv2 tunnels, or for L2TPv3 tunnels,
could result in L2TPv3 packets being transmitted which are not
compliant with L2TPv3 RFC3931. This patch series removes the support
for configurable offsets.

No known userspace l2tp daemon configures an offset. However,
iproute2's "ip l2tp" command has an offset parameter and if set, the
value is passed to the kernel. This is the most likely use case where
offsets might be configured, e.g.

   ip l2tp add tunnel local 1.1.1.1 remote 1.1.1.2 tunnel_id 1 \
       peer_tunnel_id 2 encap ip
   ip l2tp add session name l2tp0 tunnel_id 1 session_id 1 \
       peer_session_id 2 offset 8

The above would result in packets being transmitted to 1.1.1.2 with 8
bytes padding between the L2TPv3 header and the payload. The peer
would need to be configured with the same offset value. However, the
packets are not compliant with the L2TPv3 RFC, hence I think it's
unlikely that offset is being used. With this patch series applied,
the offset would not be configured. The peer would need to be modified to
remove its offset setting too.

iproute2 should be modified to remove or ignore the ip l2tp offset
parameter.

This issue was discovered when reviewing a patch series from
lorenzo.bianconi@redhat.com which adds another netlink attribute to
configure the expected offset in received L2TPv3 packets. This change
is reverted by this series because offsets do not exist in L2TPv3
packets. These commits are:

  commit f15bc54eee ("l2tp: add peer_offset parameter")
  commit 820da53575 ("l2tp: fix missing print session offset info")

In more detail:

The L2TPv2 protocol supports a variable offset from the L2TPv2 header
to the payload to give the sender implementation some flexibility for
data alignment when adding L2TP headers on to payloads. The offset
value is indicated by an optional field in the L2TP header.  Our L2TP
implementation already detects the presence of the optional offset in
received packets and skips those bytes when parsing packets. All
transmitted L2TPv2 packets are always transmitted with no offset.

L2TPv3 has no optional offset field in the L2TPv3 packet
header. Instead, L2TPv3 defines optional fields in a "Layer-2 Specific
Sublayer". At the time when the original L2TP code was written, there
was talk at IETF of offset being implemented in a new Layer-2 Specific
Sublayer. A L2TP_ATTR_OFFSET netlink attribute was added so that this
offset could be configured and the intention was to allow it to be
also used to set the tx offset for L2TPv2. However, no L2TPv3 offset
was ever specified and the L2TP_ATTR_OFFSET parameter was forgotten
about.

Setting L2TP_ATTR_OFFSET results in L2TPv3 packets being transmitted
with the specified number of bytes padding between L2TPv3 header and
payload. This is not compliant with L2TPv3 RFC3931. So this change
removes the configurable offset altogether while retaining
L2TP_ATTR_OFFSET in the API for backwards compatibility. If
L2TP_ATTR_OFFSET is given, its value is now silently ignored.
====================

Reviewed-by: Guillaume Nault <g.nault@alphalink.fr>
Tested-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
2018-01-05 11:03:42 -05:00
arch s390/diag: add diag26c support for VNIC info 2018-01-02 13:52:23 -05:00
block block-throttle: avoid double charge 2017-12-20 11:10:17 -07:00
certs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2017-12-22 12:22:48 -08:00
Documentation Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-12-29 15:42:26 -05:00
drivers net/mlx5e: hide an unused variable 2018-01-05 10:55:34 -05:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-12-29 15:42:26 -05:00
include l2tp: add comment in API header that L2TP_ATTR_OFFSET is not used 2018-01-05 11:03:26 -05:00
init Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-12-23 11:53:04 -08:00
ipc Rename superblock flags (MS_xyz -> SB_xyz) 2017-11-27 13:05:09 -08:00
kernel Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-12-29 15:42:26 -05:00
lib Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-12-22 11:16:31 -05:00
mm Merge branch 'for-linus' of git://git.kernel.dk/linux-block 2017-12-21 11:13:37 -08:00
net l2tp: remove configurable payload offset 2018-01-05 11:03:19 -05:00
samples Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2017-12-18 10:51:06 -05:00
scripts Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-12-15 11:44:59 -08:00
security Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-12-16 22:11:55 -05:00
sound ALSA: hda - Fix missing COEF init for ALC225/295/299 2017-12-27 08:53:59 +01:00
tools selftests: rtnetlink: add erspan and ip6erspan 2018-01-02 13:37:42 -05:00
usr initramfs: fix initramfs rebuilds w/ compression after disabling 2017-11-03 07:39:19 -07:00
virt KVM/ARM Fixes for v4.15, Round 2 2017-12-18 12:57:43 +01:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild misc updates for v4.15 2017-11-17 17:51:33 -08:00
.mailmap Add Jason Gunthorpe as co-maintainer of the RDMA stack 2017-11-17 09:36:18 -08:00
COPYING
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS batman-adv: Convert packet.h to uapi header 2017-12-21 15:35:53 -05:00
Makefile Linux 4.15-rc5 2017-12-23 20:47:16 -08:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.