[RFC] Crazy idea for deferring hosts in progress to a later hostgroup

[Daniel Miller <bonsaiviking () gmail com>]

List,

This is a crazy idea, but I think it might work. First, the problem: Nmap
(portscan phase) scans hosts in a large group (hostgroup), and while some
hosts may finish quickly, a few slow systems may drag on for a long time,
preventing new hosts from being scanned until they are finished.

I propose that these slow hosts be identified and "frozen," then added to
the next hostgroup to be scanned. This way, new (potentially fast) hosts
can be scanned while these slow ones are finishing.

Here are the challenges I see to this approach:

1. The data structure for a "host being scanned" is the HostScanStats
(HSS), which has a UltraScanInfo (USI) as a data member. This USI is
different for each run of the ultrascan engine (hostgroup), so the
"freezing" and "thawing" would have to be able to replace this and any
related data members without losing results or timing info.

2. Hostgroups are defined not only by strict numbers (e.g. we have 1024 new
hosts, that's one hostgroup), but also by other factors like connectedness
(e.g. a directly-connected IP will be put into a different hostgroup from
those that require IP routing). So if a slow host is deferred, the next
hostgroup to be scanned may not be appropriate for it to be in.

3. Multiple scan types can be used in one scan (e.g. -sSU) which is
implemented as subsequent calls to ultrascan. If a HSS is deferred in the
SYN scan phase, should its Target be started in the UDP scan phase, or
should the entire Target be deferred to the next hostgroup? I tend to think
it should be allowed to start the UDP scan phase, but this would have to be
engineered.

4. What determines a "slow host"? Should there be a numeric limit on how
many can be deferred? On how many deferrals can happen for one host?

I'd really like to hear your feedback on this idea. Thanks!

Dan

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