netdev - Problem with xfrm interface and bridged devices

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Date:   Thu, 26 Jan 2023 09:43:57 +0100
From:   Wolfgang Nothdurft <wolfgang@...ogate.de>
To:     Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org
Subject: Problem with xfrm interface and bridged devices

Hi there,

when using a xfrm interface in a bridged setup (the outgoing device is 
bridged), the incoming packets in the xfrm interface inherit the bridge 
info and confuses the netfilter connection tracking.

brctl show
bridge name     bridge id               STP enabled     interfaces
br_eth1         8000.000c29fe9646       no              eth1

This messes up the connection tracking so that only the outgoing packets 
shows up and the connections through the xfrm interface are UNREPLIED. 
When using stateful netfilter rules, the response packet will be blocked 
as state invalid.

telnet 192.168.12.1 7
Trying 192.168.12.1...

conntrack -L
tcp      6 115 SYN_SENT src=192.168.11.1 dst=192.168.12.1 sport=52476 
dport=7 packets=2 bytes=104 [UNREPLIED] src=192.168.12.1 
dst=192.168.11.1 sport=7 dport=52476 packets=0 bytes=0 mark=0 
secctx=system_u:object_r:unlabeled_t:s0 use=1

Chain INPUT (policy DROP 0 packets, 0 bytes)
     2   104 DROP_invalid  all  --  *      *       0.0.0.0/0 
0.0.0.0/0            state INVALID

Jan 26 09:28:12 defendo kernel: fw-chk drop [STATE=invalid] IN=ipsec0 
OUT= PHYSIN=eth1 MAC= SRC=192.168.12.1 DST=192.168.11.1 LEN=52 TOS=0x00 
PREC=0x00 TTL=64 ID=0 DF PROTO=TCP SPT=7 DPT=52476 WINDOW=64240 RES=0x00 
ACK SYN URGP=0 MARK=0x1000000

The attached patch removes the bridge info from the incoming packets on 
the xfrm interface, so the packet can be properly assigned to the 
connection.

Kind Regards,
Wolfgang
View attachment "remove_inherited_bridge_info_from_skb.patch" of type "text/x-patch" (512 bytes)