Re: [PATCH mptcp-next] selftests: mptcp: use offset to match RM_ADDR message

[Matthieu Baerts <matttbe@kernel.org>]

Hi Hangbin,

Thank you for the follow-up!

On 08/10/2026 12:06, Hangbin Liu wrote:
> From: Hangbin Liu <liuhangbin@kylinos.cn>
> 
> nft cannot match RM_ADDR when it is the second MPTCP option,

Do you mind adding a short explanation why or just a ref to:

 https://lore.kernel.org/a391d81c-0bce-41e6-886e-a558765c6891@kernel.org

Also, could you title this patch:

  Squash to "selftests: mptcp: convert iptables to nftables for
  mptcp_join.sh"

And mention what should be added to the original commit message, please?

> so we rely on hard-coded offsets. A tcpdump capture of the RM_ADDR
> message looks like:
> 
>   [TCP header: 20 bytes] [nop] [nop] [timestamp: 10 bytes] \
>         [MPTCP DSS: 12 bytes] [MPTCP RM_ADDR: 4 bytes]
> 
> We verify: TCP Data Offset (TCP[12] × 8) equals 48 bytes (12 x 4),
> DSS length (TCP[33] x 8) is 12 bytes, and RM_ADDR subtype (TCP[46] × 8)
> is 4. This matches the old cBPF check, which calculated offsets starting
> from the IP header:
> 
> (ip[32] & 0xf0) == 0xc0 && ip[53] == 0x0c && (ip[66] & 0xf0) == 0x40
> 
> Also add MPTCP kind (30) checks for the DSS (TCP[32] x 8) and RM_ADDR
> (TCP[44] x 8) options.

Good idea.

> 
> Signed-off-by: Hangbin Liu <liuhangbin@kylinos.cn>
> ---
>  tools/testing/selftests/net/mptcp/mptcp_join.sh | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
> index b16e24418e73..194b80277ae2 100755
> --- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
> +++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
> @@ -4375,7 +4375,12 @@ endpoint_tests()
>  		local nft=1
>  		ip netns exec "${ns2}" nft insert rule ip filter OUTPUT \
>  			ip saddr 10.0.1.2 meta l4proto tcp \
> -			tcp option mptcp subtype remove-addr drop || nft=0
> +			@th,96,4 == 12 \
> +			@th,256,8 == 30 \
> +			@th,264,8 == 12 \
> +			@th,352,8 == 30 \
> +			@th,368,4 == 4 \
> +			drop || nft=0
>  		local i
>  		for i in $(seq 3); do
>  			pm_nl_del_endpoint $ns2 1 10.0.1.2
> @@ -4454,7 +4459,12 @@ endpoint_tests()
>  		local nft=1
>  		ip netns exec "${ns1}" nft insert rule ip filter OUTPUT \
>  			ip saddr 10.0.1.1 meta l4proto tcp \
> -			tcp option mptcp subtype remove-addr drop || nft=0
> +			@th,96,4 == 12 \
> +			@th,256,8 == 30 \
> +			@th,264,8 == 12 \
> +			@th,352,8 == 30 \
> +			@th,368,4 == 4 \

Do you mind just adding this sequence to a global variable (an array?),
similar to what was done before with the cBPF filter, with a short
comment, please?

That would be easier to understand here, and to avoid duplicated code.

> +			drop || nft=0
>  		pm_nl_del_endpoint $ns1 42 10.0.1.1
>  		sleep 0.5
>  		chk_subflow_nr "after delete ID 0" 2
> 
> ---
> base-commit: 9651c766735c19e7a6b90d731bab53ef7959def8
> change-id: 20261008-mptcp_rm_addr-92ab7ff3d94d
> 
> Best regards,

Cheers,
Matt
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