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Mathieu Desnoyers e1e84eb58e ipv4/icmp: l3mdev: Perform icmp error route lookup on source device routing table (v2) 
As per RFC792, ICMP errors should be sent to the source host.

However, in configurations with Virtual Routing and Forwarding tables,
looking up which routing table to use is currently done by using the
destination net_device.

commit 9d1a6c4ea4 ("net: icmp_route_lookup should use rt dev to
determine L3 domain") changes the interface passed to
l3mdev_master_ifindex() and inet_addr_type_dev_table() from skb_in->dev
to skb_dst(skb_in)->dev. This effectively uses the destination device
rather than the source device for choosing which routing table should be
used to lookup where to send the ICMP error.

Therefore, if the source and destination interfaces are within separate
VRFs, or one in the global routing table and the other in a VRF, looking
up the source host in the destination interface's routing table will
fail if the destination interface's routing table contains no route to
the source host.

One observable effect of this issue is that traceroute does not work in
the following cases:

- Route leaking between global routing table and VRF
- Route leaking between VRFs

Preferably use the source device routing table when sending ICMP error
messages. If no source device is set, fall-back on the destination
device routing table. Else, use the main routing table (index 0).

[ It has been pointed out that a similar issue may exist with ICMP
  errors triggered when forwarding between network namespaces. It would
  be worthwhile to investigate, but is outside of the scope of this
  investigation. ]

[ It has also been pointed out that a similar issue exists with
  unreachable / fragmentation needed messages, which can be triggered by
  changing the MTU of eth1 in r1 to 1400 and running:

  ip netns exec h1 ping -s 1450 -Mdo -c1 172.16.2.2

  Some investigation points to raw_icmp_error() and raw_err() as being
  involved in this last scenario. The focus of this patch is TTL expired
  ICMP messages, which go through icmp_route_lookup.
  Investigation of failure modes related to raw_icmp_error() is beyond
  this investigation's scope. ]

Fixes: 9d1a6c4ea4 ("net: icmp_route_lookup should use rt dev to determine L3 domain")
Link: https://tools.ietf.org/html/rfc792
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2020-10-14 17:14:11 -07:00
arch xen: branch for v5.9-rc9 2020-10-08 11:01:53 -07:00
block block-5.9-2020-10-02 2020-10-02 14:34:52 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2020-08-30 15:53:44 -07:00
Documentation docs: networking: update XPS to account for netif_set_xps_queue 2020-10-13 16:21:54 -07:00
drivers net: fec: Fix phy_device lookup for phy_reset_after_clk_enable() 2020-10-12 14:16:30 -07:00
fs Description for this pull request: 2020-10-08 11:10:13 -07:00
include netfilter: nf_log: missing vlan offload tag and proto 2020-10-14 01:25:14 +02:00
init bootconfig: init: make xbc_namebuf static 2020-09-18 22:17:05 -04:00
ipc ipc: adjust proc_ipc_sem_dointvec definition to match prototype 2020-09-05 12:14:29 -07:00
kernel Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-10-08 14:11:21 -07:00
lib drm-misc-fixes for v5.9: 2020-10-06 12:38:28 +10:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm mm: avoid early COW write protect games during fork() 2020-10-08 10:11:32 -07:00
net ipv4/icmp: l3mdev: Perform icmp error route lookup on source device routing table (v2) 2020-10-14 17:14:11 -07:00
samples treewide: Use fallthrough pseudo-keyword 2020-08-23 17:36:59 -05:00
scripts scripts/spelling.txt: fix malformed entry 2020-10-03 11:28:12 -07:00
security device_cgroup RCU warning fix from Amol Grover <frextrite@gmail.com> 2020-09-15 16:26:57 -07:00
sound sound fixes for 5.9-rc7 2020-09-24 09:00:05 -07:00
tools selftests: netfilter: extend nfqueue test case 2020-10-12 01:59:40 +02:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt KVM: fix memory leak in kvm_io_bus_unregister_dev() 2020-09-11 13:15:11 -04:00
.clang-format clang-format: Update with the latest for_each macro list 2020-09-01 12:53:42 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: Add ZSTD-compressed files 2020-07-31 11:50:49 +02:00
.mailmap mailmap: add older email addresses for Kees Cook 2020-09-19 13:13:38 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS CREDITS: Replace HTTP links with HTTPS ones 2020-07-23 14:53:58 -06:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS drm fixes for 5.9 final 2020-10-06 11:05:44 -07:00
Makefile Linux 5.9-rc8 2020-10-04 16:04:34 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

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

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

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.