Hello Jon
> Hi again
> 
> So my 'blinder' project is moving along. I got (almost) everything in
> working order. I still need to do a couple of things before I start
> cleaning up, and move everything into the 'proper' fhs-locations. But
> none of that is really all that complicated.
> There is one obstacle remaining, however, that I *am* going to need help
> with.
> 
> Using the weblet and some cgi-scripts I can now generate a crontab which
> includes the original content, and has some entries added that will call
> the programs to open/close my blinds at designated times.
> 
> For a number of reasons I decided to generate this file in a temporary
> location, as opposed to try and edit /etc/crontab on the fly. It works,
> and reliably generates the file as it should look.
> 
> My problem at this stage is getting the generated file inserted into the
> system. Because of the (very sensible) fact that cgi-scripts may not
> write to crontab, and setting suid on the script doesn't work either,
> I'm kind of stumped on how to achieve this.
1. As you are not afraid for security problems you could solve this rather easy by 
changeing the user running the sh-httpd to root.
change the   
www     stream  tcp     nowait  sh-httpd        /usr/sbin/tcpd  /usr/sbin/sh-httpd 
to 
www stream tcp nowait root ....................
and restart inetd

.....................
2. second possibility create a cron job that looks for an alternative crontab at 
regular 
intervals and insert this alternative one in the  main crontab.
-----------------------------------------
3. make a small c-script that reads your alternative file, and writes it to crontab.
This file can be owned by root.  suid 4755 
execute this file from a special page or option in cgi-bin  
 ......................................................
> Questions:
> Is there a sensible way to let a cgi-script update crontab? Without
> opening ridiculous security issues, like hacking sh-httpd to let cgi
> execute outside of cgi-bin...
> 

> Does cron allow for 'sourcing' of additional files from /etc/crontab?
> (Like adding a: . /path/to/sh-httpd/writeable/file to /etc/crontab)
look above
> 
> Can I have cron look at a (different) crontab that is writeable by 
> sh-httpd?
yes see above
> Most of the programming that I've already done is probably full of
> security issues, as it is, but I don't worry too much about that (yet), as the
> whole thing is well shielded from the Net. Evenso, I'd rather avoid
> having to open up the system even further.
> 
> If anyone is curious, there's a dummy version of the form that I built
> at http://bund.dk/~jon/blinder somewhere. And the function that's my
> problem is with the "Commit Changes"-button... Never mind the colors/layout,
> though, "I'm *not* a web-programmer" ;-P
> 
> I know this is borderline [OT], but I figure this list is my best bet at
> getting some useful tips on this. Sorry if I'm being a nuisance, but
> well...
> 
> TIA
> 
> Jon Clausen
regards

Eric Wolzak
member of the Bering crew.


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