Date: Mon, 31 Aug 1998 13:26:28 -0700 From: bmah@CA.Sandia.GOV (Bruce A. Mah) To: Don Lewis <Don.Lewis@tsc.tdk.com> Cc: bmah@california.sandia.gov, Tristan Horn <tristan+-eyixqg@ETHEREAL.NET>, BUGTRAQ@netspace.org, security@FreeBSD.ORG Subject: Re: FreeBSD's RST validation Message-ID: <199808312026.NAA24999@stennis.ca.sandia.gov> In-Reply-To: Your message of "Mon, 31 Aug 1998 11:55:07 PDT." <199808311855.LAA28095@salsa.gv.tsc.tdk.com>
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If memory serves me right, Don Lewis wrote:
> On Aug 31, 11:24am, Bruce A. Mah wrote:
[snip]
> } if (tiflags & TH_RST) {
> } ! if ((tiflags & TH_ACK) &&
> } ! /* XXX outside window? XXX */
> } ! (SEQ_GT(ti->ti_ack, tp->iss) &&
> } ! SEQ_LEQ(ti->ti_ack, tp->snd_max)))
> } tp = tcp_drop(tp, ECONNREFUSED);
> } goto drop;
> } }
>
> As more data is sent across the connection, the wider the window for
> a spoofed RST opens. Once you send 2 GB, legitimate RSTs no longer
> work. You should probably be comparing against tp->snd_una instead
> of tp->iss.
Hmmm. I was thinking specifically of the problem that with a RST arriving for
a connection in SYN_SENT, the ACK in the RST-bearing segment has to
acknowledge the initial SYN (thus, a test against tp->iss). I hadn't thought
that the ever-increasing difference between tp->snd_una and tp->iss would be a
problem, since at this point in the code, we know that the receiving end of
the connection is in SYN_SENT, as opposed to, say, ESTABLISHED. Shouldn't
(tp->snd_una == tp->iss) in this state, in which case, either would do? (Not
trying to split hairs, but just trying to learn a little more.)
Thanks,
Bruce.
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