mptcp: pm: re-using ID of unused flushed subflows

If no subflows are attached to the 'subflow' endpoints that are being
flushed, the corresponding addr IDs will not be marked as available
again.

Mark all ID as being available when flushing all the 'subflow'
endpoints, and reset local_addr_used counter to cover these cases.

Note that mptcp_pm_remove_addrs_and_subflows() helper is only called for
flushing operations, not to remove a specific set of addresses and
subflows.

Fixes: 06faa22 ("mptcp: remove multi addresses and subflows in PM")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20240819-net-mptcp-pm-reusing-id-v1-5-38035d40de5b@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: matttbe

net/mptcp/pm_netlink.c

@@ -1623,8 +1623,15 @@ static void mptcp_pm_remove_addrs_and_subflows(struct mptcp_sock *msk,
 		mptcp_pm_remove_addr(msk, &alist);
 		spin_unlock_bh(&msk->pm.lock);
 	}
+
 	if (slist.nr)
 		mptcp_pm_remove_subflow(msk, &slist);
+
+	/* Reset counters: maybe some subflows have been removed before */
+	spin_lock_bh(&msk->pm.lock);
+	bitmap_fill(msk->pm.id_avail_bitmap, MPTCP_PM_MAX_ADDR_ID + 1);
+	msk->pm.local_addr_used = 0;
+	spin_unlock_bh(&msk->pm.lock);
 }
 
 static void mptcp_nl_remove_addrs_list(struct net *net,