Re: pingflood.c

[pedward () WEBCOM COM (pedward () WEBCOM COM)]

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.  /\