Re: [PATCH mptcp-next] mptcp: pm: in-kernel: remove mptcp_pm_has_addr_attr_id

[Matthieu Baerts <matttbe@kernel.org>]

Hello,

On 23/02/2026 18:35, Matthieu Baerts (NGI0) wrote:
> There is no need to call this helper: it will check if the address ID
> attribute is set, but this attribute has already been parsed previously.
> 
> Indeed, the value has been set in 'entry->addr.id' if it was set and
> positive, which is what we were looking at. Then only looking at this
> already parsed value is enough, not need to re-extract all Netlink
> attributes again.
Linked to my message on the same patch sent to netdev [1] ...

 https://lore.kernel.org/070ec312-4836-4220-b03f-07c14f1f5470@kernel.org

... I suggest replacing the commit title and message here:

------------------------- 8< -------------------------
Revert "mptcp: add needs_id for netlink appending addr"

This commit was originally adding the ability to add MPTCP endpoints
with ID 0 by accident. The in-kernel PM, handling MPTCP endpoints at the
net namespace level, is not supposed to handle endpoints with such ID,
because this ID 0 is reserved to the initial subflow as mentioned in the
MPTCPv1 protocol, a per-connection setting.

Note that 'ip mptcp endpoint add id 0' stops early with an error, but
other tools might still ask to create MPTCP endpoint with the ID 0.

In other words, it was wrong to call the mptcp_pm_has_addr_attr_id
helper to check whether the address ID attribute is set: if it was set
to 0, a new MPTCP endpoint would be created with ID 0, which is not
expected, and might cause various issues later (even if in most cases,
such endpoint is ignored).

Fixes: 584f38942626 ("mptcp: add needs_id for netlink appending addr")
------------------------- 8< -------------------------

Any objections?

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.