Re: [PATCH v2] udp: avoid ufo handling on IP payload compression packets

[David Miller <davem@davemloft.net>]

From: Alexey Kodanev <alexey.kodanev@oracle.com>
Date: Thu,  9 Mar 2017 13:56:46 +0300

> commit c146066ab802 ("ipv4: Don't use ufo handling on later transformed
> packets") and commit f89c56ce710a ("ipv6: Don't use ufo handling on
> later transformed packets") added a check that 'rt->dst.header_len' isn't
> zero in order to skip UFO, but it doesn't include IPcomp in transport mode
> where it equals zero.
> 
> Packets, after payload compression, may not require further fragmentation,
> and if original length exceeds MTU, later compressed packets will be
> transmitted incorrectly. This can be reproduced with LTP udp_ipsec.sh test
> on veth device with enabled UFO, MTU is 1500 and UDP payload is 2000:
> 
> * IPv4 case, offset is wrong + unnecessary fragmentation
>     udp_ipsec.sh -p comp -m transport -s 2000 &
>     tcpdump -ni ltp_ns_veth2
>     ...
>     IP (tos 0x0, ttl 64, id 45203, offset 0, flags [+],
>       proto Compressed IP (108), length 49)
>       10.0.0.2 > 10.0.0.1: IPComp(cpi=0x1000)
>     IP (tos 0x0, ttl 64, id 45203, offset 1480, flags [none],
>       proto UDP (17), length 21) 10.0.0.2 > 10.0.0.1: ip-proto-17
> 
> * IPv6 case, sending small fragments
>     udp_ipsec.sh -6 -p comp -m transport -s 2000 &
>     tcpdump -ni ltp_ns_veth2
>     ...
>     IP6 (flowlabel 0x6b9ba, hlim 64, next-header Compressed IP (108)
>       payload length: 37) fd00::2 > fd00::1: IPComp(cpi=0x1000)
>     IP6 (flowlabel 0x6b9ba, hlim 64, next-header Compressed IP (108)
>       payload length: 21) fd00::2 > fd00::1: IPComp(cpi=0x1000)
> 
> Fix it by checking 'rt->dst.xfrm' pointer to 'xfrm_state' struct, skip UFO
> if xfrm is set. So the new check will include both cases: IPcomp and IPsec.
> 
> Fixes: c146066ab802 ("ipv4: Don't use ufo handling on later transformed packets")
> Fixes: f89c56ce710a ("ipv6: Don't use ufo handling on later transformed packets")
> Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
> ---
> 
> v2: use dst_xfrm() to access xfrm_state

Applied and queued up for -stable, thanks!