Re: [PATCH 01/11] rxrpc: Add a common object cache

From: David Howells
Date: Tue Mar 08 2016 - 16:11:24 EST

David Miller <davem@xxxxxxxxxxxxx> wrote:

> > One could argue, I suppose, that things should've been arranged that the
> > RxRPC client would manage the lifetime of each connection it sets up,
> > rather than both ends letting it lapse by mutual loss of interest. But
> > you *still* have to have a timeout, lest the client die and not close its
> > connection.
> But the point is if there is no limitation on the number of these connections
> that can be setup.... wait for troubles.
> And if you try to put in some kind of limit to handle this, it's then
> easy for the bad guy to block out other legitimate users.

I can put in a limit per peer, where a 'peer' is either a particular remote
UDP port or particulat remote host. TCP has this by virtue of having a
limited number of ports available per IP address. But if I have 10 IP
addresses available, I can attempt to set up half a million TCP connections to
a server simultaneously. If I have access to a box that has an NFS mount on
it, I can potentially open sufficient TCP ports that the NFS mount can't make
a connection if it's not allowed to use privileged ports.

Am I right in thinking that you have decided that it can't be done and
shouldn't be done?