Patrick McHardy wrote:
Evgeniy Polyakov wrote:
On Tue, Jul 01, 2008 at 01:53:43PM +0200, Patrick McHardy
(kaber@xxxxxxxxx) wrote:
My two main objections are that this only works for TCP and
can be trivially evaded. What use cases does it have?
Yes, it is TCP specific module.
What about the use cases? I certainly like the idea you suggest in
your blog ("Ever dreamt to block all Linux users in your network
from accessing internet and allow full bandwidth to Windows worm?")
:) But something this easy to evade doesn't seem to provide a real
benefit for a firewall.
I can see that something like "Block IE6 running on Windows version X"
might be useful (NUFW can do this I think), but that needs support
from the host.
Not addressing Evgeniy's module but speaking generally...
It sure would be nice for regular socket applications to have an easy,
unprivileged way to query the OS fingerprint information of a given socket.
Speaking purely from a userspace application API perspective, it would
be most useful for an app to be able to stop OSF collection, start OSF
collection, and query OSF stats. start/stop would be a refcount that
disables in-kernel OSF when not in use.
To present a specific use case: I would like to know if incoming SMTP
connections are Windows or not. That permits me to better determine if
the incoming connection is a hijacked PC or not -- it becomes a useful
factor in spamassassin scoring.
In this case, incoming SMTP is -always- TCP, thus being a TCP-specific
module is not a problem. You cover a huge swath of apps even if the
module is TCP-specific.
Another use case is validating whether a browser is "lying" about its
OS, when parsing HTTP user-agent info, or in general when any remote
agent is "lying" about its OS. Security software can use that as an
additional red-flag factor.
Jeff
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