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Florian Westphal 12e10b1212 net: ip: always refragment ip defragmented packets
[ Upstream commit bb4cc1a188 ]

Conntrack reassembly records the largest fragment size seen in IPCB.
However, when this gets forwarded/transmitted, fragmentation will only
be forced if one of the fragmented packets had the DF bit set.

In that case, a flag in IPCB will force fragmentation even if the
MTU is large enough.

This should work fine, but this breaks with ip tunnels.
Consider client that sends a UDP datagram of size X to another host.

The client fragments the datagram, so two packets, of size y and z, are
sent. DF bit is not set on any of these packets.

Middlebox netfilter reassembles those packets back to single size-X
packet, before routing decision.

packet-size-vs-mtu checks in ip_forward are irrelevant, because DF bit
isn't set.  At output time, ip refragmentation is skipped as well
because x is still smaller than the mtu of the output device.

If ttransmit device is an ip tunnel, the packet size increases to
x+overhead.

Also, tunnel might be configured to force DF bit on outer header.

In this case, packet will be dropped (exceeds MTU) and an ICMP error is
generated back to sender.

But sender already respects the announced MTU, all the packets that
it sent did fit the announced mtu.

Force refragmentation as per original sizes unconditionally so ip tunnel
will encapsulate the fragments instead.

The only other solution I see is to place ip refragmentation in
the ip_tunnel code to handle this case.

Fixes: d6b915e29f ("ip_fragment: don't forward defragmented DF packet")
Reported-by: Christian Perle <christian.perle@secunet.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2021-01-17 14:05:32 +01:00
Documentation x86/CPU/AMD: Save AMD NodeId as cpu_die_id 2020-12-30 11:51:47 +01:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch x86/asm/32: Add ENDs to some functions and relabel with SYM_CODE_* 2021-01-17 14:05:30 +01:00
block scsi: block: Fix a race in the runtime power management code 2021-01-06 14:48:37 +01:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto crypto: asym_tpm: correct zero out potential secrets 2021-01-12 20:16:17 +01:00
drivers net/sonic: Fix some resource leaks in error handling paths 2021-01-17 14:05:31 +01:00
fs btrfs: send: fix wrong file path when there is an inode with a pending rmdir 2021-01-12 20:16:23 +01:00
include vfio iommu: Add dma available capability 2021-01-17 14:05:30 +01:00
init exec: Transform exec_update_mutex into a rw_semaphore 2021-01-09 13:44:55 +01:00
ipc ipc/util.c: sysvipc_find_ipc() incorrectly updates position index 2020-05-20 08:20:16 +02:00
kernel workqueue: Kick a worker based on the actual activation of delayed works 2021-01-12 20:16:09 +01:00
lib lib/genalloc: fix the overflow when size is too big 2021-01-12 20:16:10 +01:00
mm mm: don't wake kswapd prematurely when watermark boosting is disabled 2020-12-30 11:51:27 +01:00
net net: ip: always refragment ip defragmented packets 2021-01-17 14:05:32 +01:00
samples samples: bpf: Fix lwt_len_hist reusing previous BPF map 2020-12-30 11:51:12 +01:00
scripts depmod: handle the case of /sbin/depmod without /sbin in PATH 2021-01-12 20:16:10 +01:00
security ima: Don't modify file descriptor mode on the fly 2020-12-30 11:51:39 +01:00
sound ALSA: hda/realtek: Add two "Intel Reference board" SSID in the ALC256. 2021-01-12 20:16:23 +01:00
tools tools: selftests: add test for changing routes with PTMU exceptions 2021-01-17 14:05:32 +01:00
usr initramfs: restore default compression behavior 2020-04-08 09:08:38 +02:00
virt kvm: check tlbs_dirty directly 2021-01-12 20:16:22 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap ARM: SoC fixes 2019-11-10 13:41:59 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS Documentation/llvm: add documentation on building w/ Clang/LLVM 2020-08-26 10:40:46 +02:00
Makefile Linux 5.4.89 2021-01-12 20:16:25 +01:00
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.