Re: [PATCH mptcp-net v3 3/8] mptcp: pm: userspace: ID0 is not part of local_addr_used

[Geliang Tang <geliang@kernel.org>]

Hi Matt,

On Fri, 2026-08-07 at 10:41 +0200, Matthieu Baerts (NGI0) wrote:
> The PM's local_addr_used counter doesn't take into account the ID0,
> similar to what is done with the in-kernel PM.
> 
> When deleting a local address, only decrement the counter if it is
> not
> linked to the (initial) ID0. Similarly, do not increment it when
> re-adding the exact same entry.
> 
> Fixes: 77e4b94a3de6 ("mptcp: update userspace pm infos")
> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
> ---
> v3:
>  - split from patch 1.
>  - do the same check when incrementing it to avoid a "leak".
> (Sashiko)
>  - use a new dedicated helper, clearer.
> ---
>  net/mptcp/pm_userspace.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/net/mptcp/pm_userspace.c b/net/mptcp/pm_userspace.c
> index 3f1471ec3fc7..27fed3519d39 100644
> --- a/net/mptcp/pm_userspace.c
> +++ b/net/mptcp/pm_userspace.c
> @@ -27,6 +27,12 @@ void
> mptcp_userspace_pm_free_local_addr_list(struct mptcp_sock *msk)
>  	}
>  }
>  
> +static bool
> +is_init_id0(struct mptcp_pm_addr_entry *entry)

nit: The function is quite short, so no line wrapping is needed.

Thanks,
-Geliang

> +{
> +	return entry->addr.id == 0 && entry->addr.port == 0;
> +}
> +
>  static struct mptcp_pm_addr_entry *
>  mptcp_userspace_pm_lookup_addr(struct mptcp_sock *msk,
>  			       const struct mptcp_addr_info *addr)
> @@ -95,7 +101,9 @@ static int
> mptcp_userspace_pm_append_new_local_addr(struct mptcp_sock *msk,
>  							MPTCP_PM_MAX
> _ADDR_ID + 1,
>  							1);
>  		list_add_tail_rcu(&e->list, &msk-
> >pm.userspace_pm_local_addr_list);
> -		msk->pm.local_addr_used++;
> +		/* Just to avoid this counter not to decrease when
> deleted */
> +		if (!is_init_id0(e))
> +			msk->pm.local_addr_used++;
>  		ret = e->addr.id;
>  	} else if (addr_match && id_match) {
>  		ret = entry->addr.id;
> @@ -121,12 +129,15 @@ static int
> mptcp_userspace_pm_delete_local_addr(struct mptcp_sock *msk,
>  	if (!entry)
>  		return -EINVAL;
>  
> +	/* The initial address ID doesn't increment local_addr_used
> */
> +	if (!is_init_id0(entry))
> +		msk->pm.local_addr_used--;
> +
>  	/* TODO: a refcount is needed because the entry can
>  	 * be used multiple times (e.g. fullmesh mode).
>  	 */
>  	list_del_rcu(&entry->list);
>  	sock_kfree_s(sk, entry, sizeof(*entry));
> -	msk->pm.local_addr_used--;
>  	return 0;
>  }
>