Re: [PATCH] xfrm: fix tunnel model fragmentation behavior
flat view
From: Steffen Klassert <steffen.klassert@secunet.com>
Date: 2022-02-21 11:19:47
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On Mon, Feb 21, 2022 at 01:16:48PM +0800, Lina Wang wrote:
in tunnel mode, if outer interface(ipv4) is less, it is easily to let
inner IPV6 mtu be less than 1280. If so, a Packet Too Big ICMPV6 message
is received. When send again, packets are fragmentized with 1280, they
are still rejected with ICMPV6(Packet Too Big) by xfrmi_xmit2().
According to RFC4213 Section3.2.2:
if (IPv4 path MTU - 20) is less than 1280
if packet is larger than 1280 bytes
Send ICMPv6 "packet too big" with MTU = 1280.
Drop packet.
else
Encapsulate but do not set the Don't Fragment
flag in the IPv4 header. The resulting IPv4
packet might be fragmented by the IPv4 layer
on the encapsulator or by some router along
the IPv4 path.
endif
else
if packet is larger than (IPv4 path MTU - 20)
Send ICMPv6 "packet too big" with
MTU = (IPv4 path MTU - 20).
Drop packet.
else
Encapsulate and set the Don't Fragment flag
in the IPv4 header.
endif
endif
Packets should be fragmentized with ipv4 outer interface, so change it.
After it is fragemtized with ipv4, there will be double fragmenation.
No.48 & No.51 are ipv6 fragment packets, No.48 is double fragmentized,
then tunneled with IPv4(No.49& No.50), which obey spec. And received peer
cannot decrypt it rightly.
48 2002::10 2002::11 1296(length) IPv6 fragment (off=0 more=y ident=0xa20da5bc nxt=50)
49 0x0000 (0) 2002::10 2002::11 1304 IPv6 fragment (off=0 more=y ident=0x7448042c nxt=44)
50 0x0000 (0) 2002::10 2002::11 200 ESP (SPI=0x00035000)
51 2002::10 2002::11 180 Echo (ping) request
52 0x56dc 2002::10 2002::11 248 IPv6 fragment (off=1232 more=n ident=0xa20da5bc nxt=50)
esp_noneed_fragment has fixed above issues. Finally, it acted like below:
1 0x6206 192.168.1.138 192.168.1.1 1316 Fragmented IP protocol (proto=Encap Security Payload 50, off=0, ID=6206) [Reassembled in #2]
2 0x6206 2002::10 2002::11 88 IPv6 fragment (off=0 more=y ident=0x1f440778 nxt=50)
3 0x0000 2002::10 2002::11 248 ICMPv6 Echo (ping) request
Signed-off-by: Lina Wang <redacted>We have two commits in the ipsec tree that address a very similar issue. That is: commit 6596a0229541270fb8d38d989f91b78838e5e9da xfrm: fix MTU regression and commit a6d95c5a628a09be129f25d5663a7e9db8261f51 Revert "xfrm: xfrm_state_mtu should return at least 1280 for ipv6" Can you please doublecheck that the issue you are fixing still exist in the ipsec tree? Thanks! _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel