From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sog-mx-1.v43.ch3.sourceforge.com ([172.29.43.191] helo=mx.sourceforge.net) by sfs-ml-4.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1R8eRH-00031L-6S for bitcoin-development@lists.sourceforge.net; Tue, 27 Sep 2011 20:39:39 +0000 Received-SPF: pass (sog-mx-1.v43.ch3.sourceforge.com: domain of gmail.com designates 209.85.161.47 as permitted sender) client-ip=209.85.161.47; envelope-from=gavinandresen@gmail.com; helo=mail-fx0-f47.google.com; Received: from mail-fx0-f47.google.com ([209.85.161.47]) by sog-mx-1.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-MD5:128) (Exim 4.76) id 1R8eRG-00034c-Gv for bitcoin-development@lists.sourceforge.net; Tue, 27 Sep 2011 20:39:39 +0000 Received: by fxi1 with SMTP id 1so10719437fxi.34 for ; Tue, 27 Sep 2011 13:39:32 -0700 (PDT) MIME-Version: 1.0 Received: by 10.223.94.134 with SMTP id z6mr13026160fam.8.1317155972253; Tue, 27 Sep 2011 13:39:32 -0700 (PDT) Received: by 10.152.25.105 with HTTP; Tue, 27 Sep 2011 13:39:32 -0700 (PDT) In-Reply-To: <201109271608.07053.luke@dashjr.org> References: <201109261517.11245.luke@dashjr.org> <201109271608.07053.luke@dashjr.org> Date: Tue, 27 Sep 2011 16:39:32 -0400 Message-ID: From: Gavin Andresen To: Luke-Jr Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Spam-Score: -1.6 (-) X-Spam-Report: Spam Filtering performed by mx.sourceforge.net. See http://spamassassin.org/tag/ for more details. -1.5 SPF_CHECK_PASS SPF reports sender host as permitted sender for sender-domain 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (gavinandresen[at]gmail.com) -0.0 SPF_PASS SPF: sender matches SPF record -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature 0.0 AWL AWL: From: address is in the auto white-list X-Headers-End: 1R8eRG-00034c-Gv Cc: bitcoin-development@lists.sourceforge.net Subject: Re: [Bitcoin-development] Newly introduced DoS X-BeenThere: bitcoin-development@lists.sourceforge.net X-Mailman-Version: 2.1.9 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 27 Sep 2011 20:39:39 -0000 > @@ -1276,13 +1278,13 @@ bool CBlock::AcceptBlock() > =A0 =A0 // Get prev block index > =A0 =A0 map::iterator mi =3D > mapBlockIndex.find(hashPrevBlock); > =A0 =A0 if (mi =3D=3D mapBlockIndex.end()) > - =A0 =A0 =A0 =A0return error("AcceptBlock() : prev block not found"); > + =A0 =A0 =A0 =A0return DoS(10, error("AcceptBlock() : prev block not fou= nd")); > > > Is it certain that it cannot be triggered by a peer having some huge numb= er > more blocks than you? As I said, that is a "can't never happen but we'll wear a belt-and-suspenders just in case" case. AcceptBlock() is called from two places in the code: ProcessBlock, if the block is not an orphan: // If don't already have its previous block, shunt it off to holding area until we get it if (!mapBlockIndex.count(pblock->hashPrevBlock)) { .... orphan processing stuff... return true; } // Store to disk if (!pblock->AcceptBlock()) return error("ProcessBlock() : AcceptBlock FAILED"); The mapBlockIndex.find(hashPrevBlock) in AcceptBlock can't fail. The second place is recursively, in AcceptBlock(), processing orphans that link to the block being accepted, and mapBlockIndex.find() would find the used-to-be-an-orphan-block-that-is-now-being-accepted. So: it is a case that should be impossible to trigger. However, in case there is some subtle bug or edge case I'm not considering it seem to me keeping the check is appropriate, and, because it will be a subtle bug or edge case, it seems to me keeping the DoS penalty is also appropriate, because attackers look for subtle bugs and edge cases that can be exploited. --=20 -- Gavin Andresen