Bug in Parallel DNS resolution in Nmap 4.50?

[Lionel Cons <lionel.cons () cern ch>]

I've started a scan against a list of machines identified by their IP
addresses. The Nmap process takes 100% CPU and is stuck in the name
resolution part. I killed it after 25 minutes, which is a lot to
resolve only 400+ addresses.

Here are the last lines printed:

[...]
We got a TCP ping packet back from 192.168.74.73 port 80 (trynum = 1)
We got a TCP ping packet back from 192.168.73.75 port 80 (trynum = 1)
We got a TCP ping packet back from 192.168.21.207 port 80 (trynum = 1)
We got a ping packet back from 192.168.45.7: id = 48978 seq = 0 checksum = 16557
Completed Ping Scan at 11:20, 1.84s elapsed (436 total hosts)
mass_rdns: Using DNS server 192.168.1.5
mass_rdns: Using DNS server 192.168.1.6
Initiating Parallel DNS resolution of 436 hosts. at 11:20

And nothing after...

The scan runs fine if I add the -n option.

There must be a severe bug in the name resolution code...

Cheers,

Lionel Cons

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