Date: Mon, 29 Jul 2002 19:04:35 +0400 From: Yar Tikhiy <yar@comp.chem.msu.su> To: Ruslan Ermilov <ru@FreeBSD.ORG> Cc: net@FreeBSD.ORG Subject: Re: ftpd(8) DoS: SIZE in ASCII mode Message-ID: <20020729190435.C33729@comp.chem.msu.su> In-Reply-To: <20020726202255.GA9263@sunbay.com>; from ru@FreeBSD.ORG on Fri, Jul 26, 2002 at 11:22:55PM %2B0300 References: <20020726155745.B2089@comp.chem.msu.su> <20020726202255.GA9263@sunbay.com>
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On Fri, Jul 26, 2002 at 11:22:55PM +0300, Ruslan Ermilov wrote:
> On Fri, Jul 26, 2002 at 03:57:45PM +0400, Yar Tikhiy wrote:
> >
> > I've been pointed out by Maxim Konovalov recently that our stock
> > ftpd(8) allowed an easy DoS attack against a server running it by
> > issuing numerous "SIZE" commands on huge files when in ASCII mode.
> > In this case, ftpd(8) has to read a whole file instead of just
> > issuing a single stat(2) syscall, thus eating up the server's
> > disk bandwidth.
> >
> > The obvious solution is to disable the "SIZE" command when in ASCII
> > mode. So I'd like to ask the community whether anyone thinks there
> > must be an option to enable it back. Personally, I feel the command
> > must be disabled completely (for ASCII mode, of course) since I see
> > no good use for it at all.
> >
> How about going the lukemftpd(8) way?
>
> if (stbuf.st_size > 10240) {
> reply(550, "%s: file too large for SIZE.", filename);
> (void) fclose(fin);
> return;
> }
It looks like a nice approach at the first glance. I still doubt
type A SIZE necessity at all, but let it be this way if noone objects.
--
Yar
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