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Date:   Fri, 7 Oct 2022 14:17:51 -0700
From:   Stephen Hemminger <>
Subject: Fw: [Bug 216557] New: tcp connection not working over ip_vti

Begin forwarded message:

Date: Fri, 07 Oct 2022 20:51:12 +0000
Subject: [Bug 216557] New: tcp connection not working over ip_vti interface

            Bug ID: 216557
           Summary: tcp connection not working over ip_vti interface
           Product: Networking
           Version: 2.5
    Kernel Version: 5.15.53
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: high
          Priority: P1
         Component: IPV4
        Regression: No

TCP protocol is not working, when ipsec tunnel has been setup and ip_vti tunnel
is used for route based ipsec.

After the below changes merged with latest kernel. xfrm4_policy_check in
tcp_v4_rcv drops all packets except first syn packet under XfrmInTmplMismatch
when local destined packets are received over ip_vti tunnel.

author  Eyal Birger <>     2022-05-13 23:34:02 +0300
committer       Greg Kroah-Hartman <> 2022-05-25
09:57:30 +0200
commit  952c2464963895271c31698970e7ec1ad6f0fe45 (patch)
tree    9e8300c45a0eb5a9555eae017f8ae561f3e8bc51 /include/net/xfrm.h
parent  36d8cca5b46fe41b59f8011553495ede3b693703 (diff)
download        linux-952c2464963895271c31698970e7ec1ad6f0fe45.tar.gz
xfrm: fix "disable_policy" flag use when arriving from different devices

1) create road warrior ipsec tunnel with local ip x.x.x.x remote ip y.y.y.y.
2) create vti interface using ip tunnel add vti_test local x.x.x.x remote
y.y.y.y mode vti 
3) echo 1 > /proc/sys/net/ipv4/conf/vti_test/disable_policy
4) Add default route over vti_test.
5) ping remote ip, ping works.
6) ssh remote ip, ssh dont work. check tcp connection not working.

Root cause:
-> with above mentioned commit, now xfrm4_policy_check depends on skb's  
IPSKB_NOPOLICY flag which need to be set per skb and it only gets set in
ip_route_input_noref .

-> before above change, xfrm4_policy_check was using DST_NOPOLICY which was  
checked against dst set in skb.

-> ip_rcv_finish_core calls ip_route_input_noref only if dst is not valid in  

-> By default in kernel sysctl_ip_early_demux = 1, which means when skb with  
syn is received, tcp stack will set DST from skb to sk and in subsequent
packets it will copy dst from sk to skb and skip calling ip_route_input_nore
inside ip_rcv_finish_core.

-> so for all the subsequent  received packets, IPSKB_NOPOLICY will not get set  
and they will get drop.

only work-aroud is to disable early tcp demux.
echo 0 > /proc/sys/net/ipv4/ip_early_demux

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