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Re: Bug in Parallel DNS resolution in Nmap 4.50?
From: doug () hcsw org
Date: Fri, 21 Dec 2007 14:57:40 -0800

Hi Lionel,

On Fri, Dec 21, 2007 at 10:18:14AM +0100 or thereabouts, Lionel Cons wrote:
Here you are, two traces for two separate runs but with the same
options and same input (~600 addresses). Note the the IP addresses
have been anonymized.

Thanks for doing this! Hm.. You ran it for a couple
minutes and the last output was timestamped at about
4 seconds or so and it is in a busy loop? Very strange.

What might help a lot is a backtrace. If you have GDB
avaiable could you please try this:

$ gdb ./nmap
...

(gdb)


Then at the (gdb) prompt enter

run <your command line options>

I'll just use 600 random ones:

(gdb) run -sL -iR 600
Starting program: /home/doug/nmap/nmap-4.50/nmap -sL -iR 600

Starting Nmap 4.50 ( http://insecure.org ) at 2007-12-21 14:53 PST



Wait for it to busy loop, then hit <control-C>

Program received signal SIGINT, Interrupt.
0xb7cb59f8 in select () from /lib/tls/libc.so.6
(gdb) bt
#0  0xb7cb59f8 in select () from /lib/tls/libc.so.6
#1  0x080c32b2 in wait_for_events (ms=0x821f288, msec_timeout=309) at nsock_core.c:174
#2  0x080c4a60 in nsock_loop (nsp=0x821f288, msec_timeout=500) at nsock_core.c:979
#3  0x080a8286 in nmap_mass_rdns_core (targets=0x818ea30, num_targets=600) at nmap_dns.cc:1234
#4  0x080a8993 in nmap_mass_rdns (targets=0x1, num_targets=1) at nmap_dns.cc:1295
#5  0x08067318 in nexthost (hs=0x818e5d0, exclude_group=0x0, ports=0x814e3d0, pingtype=1) at targets.cc:614
#6  0x080626a1 in nmap_main (argc=4, argv=0xbfdfc5b4) at nmap.cc:1562
#7  0x0805e63c in main (argc=4, argv=0xbfdfc5b4) at main.cc:227


Because yours is busy looping, it probably will not
have a select() call as the top stack frame and this 
location might help track the bug down.

Thanks!

Doug

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