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Re: pingflood.c
From: pedward () WEBCOM COM (pedward () WEBCOM COM)
Date: Mon, 18 May 1998 10:23:32 -0700


The reason that this works is because many platforms implement sleep(2)
as:

alarm(seconds);
sigsuspend(...);


This is implementation is done in Solaris, etc.  I have implemented my
own sleep function because when using threads under Solaris, messing with
signals is a bad proposition.  So:

void mysleep(int seconds)
{
        struct timeval  tv;

        tv.tv_sec=seconds;
        tv.tv_usec=0;

        select(0,NULL,NULL,NULL,&tv);
}

The code above should be portable to every platform that supports the standard
select(2) semantics.  It allows for subsecond precision too.  This implementation
isn't subject to signal dainbrammage either.

--Perry

Verified it on SunOS 5.5.1. Basically, it is so simple that it
should work on any Unix box. The "bug" in ping's code is that
the code naively assumes the SIGALRM is system-generated (due
to a previous alarm() call). At least on SunOS 5.5.1, sigaction(2)
can be used to examine the source of the SIGALRM (e.g. check
that (siginfo_t *)si->si_code > 0 -- (siginfo_t *)si is returned
to the signal handler if the sa_flags member of the struct sigaction
passed to sigaction() has the SA_SIGINFO bit set). I am not sure
how this can be implemented on other systems.

BTW, how many setuid programs are there that will catch various
signals and will behave "not-as-expected" when forked off by a
signal-bomber parent process, such as pingflood?

a.varvitsiotis () iccs ntua gr                     A.Varvitsiotis
                                             ICCS Computer Center
                                      National Technical University of Athens




--
Perry Harrington        System Software Engineer    zelur xuniL  ()
http://www.webcom.com  perry.harrington () webcom com  Think Blue.  /\



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