CVE-2024-45010

In the Linux kernel, the following vulnerability has been resolved:

mptcp: pm: only mark 'subflow' endp as available

Adding the following warning ...

WARNONONCE(msk->pm.localaddrused == 0)

... before decrementing the localaddrused counter helped to find a bug when running the "remove single address" subtest from the mptcp_join.sh selftests.

Removing a 'signal' endpoint will trigger the removal of all subflows linked to this endpoint via mptcppmnlrmaddrorsubflow() with rmtype == MPTCPMIBRMSUBFLOW. This will decrement the localaddr_used counter, which is wrong in this case because this counter is linked to 'subflow' endpoints, and here it is a 'signal' endpoint that is being removed.

Now, the counter is decremented, only if the ID is being used outside of mptcppmnlrmaddrorsubflow(), only for 'subflow' endpoints, and if the ID is not 0 -- localaddrused is not taking into account these ones. This marking of the ID as being available, and the decrement is done no matter if a subflow using this ID is currently available, because the subflow could have been closed before.