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nasty things when using -T0
From: Richard Sammet <richard.sammet () sit fraunhofer de>
Date: Sun, 05 Feb 2006 15:07:07 +0100

hello everybody,

i noticed something while scanning single hosts with the -T0 timing option.

if i run nmap like:

nmap -sS -T0 -A HOST01 -vvv

it hangs at about 100% cpu usage till i send it a sig-term.

at some hosts the problem was gone if i start the same scan after stopping nmap for that host.

nmap -sS -T0 -A HOST01 -vvv
nmap -sS -T0 -A HOST01 -vvv

nmap works within normal cpu usage...

at some others (e.g. heise.de) nmap allways hangs at about 100%.

hmm... nasty.

i fired up:

strace nmap -sS -T0 -A HOST02 -vvv

which shows me that nmap always performs:

gettimeofday({1139147738, 347347}, NULL) = 0
gettimeofday({1139147738, 347367}, NULL) = 0
gettimeofday({1139147738, 347388}, NULL) = 0
gettimeofday({1139147738, 347408}, NULL) = 0
gettimeofday({1139147738, 347429}, NULL) = 0

while it hangs at about 100% cpu usage.

some infos:
Linux MYHOSTNAME #4 PREEMPT Thu Feb 2 21:56:00 CET 2006 i686 Intel(R) Pentium(R) M processor 1.80GHz GenuineIntel GNU/Linux

CFLAGS="-O3 -march=pentium4 -pipe"

gcc (GCC) 3.4.4 (Gentoo 3.4.4-r1, ssp-3.4.4-1.0, pie-8.7.8)

so long

Fraunhofer-Institut  fuer Sichere Informationstechnologie (SIT)
Fraunhofer-Institute for  Secure  Information Technology  (SIT)

Richard Sammet
Tel.:    +49 6151 869 60027
Email:   richard/./sammet\at\sit/./fraunhofer/./de
CA:      http://pki.fraunhofer.de


main(){int y=0;while(++y<7)putchar(y<2?101:y<3?45:y<4?97:y<5?120:y<6?101:10);}


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