Message-ID: <4E71F6D6.2090208@justmoon.de>
Date: Thu, 15 Sep 2011 15:00:06 +0200
From: Stefan Thomas <moon@justmoon.de>
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Subject: Re: [Bitcoin-development] Request review: drop misbehaving peers
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A few thoughts:

Should the DoS protection auto-disable if the node has less than a 
minimum number of connections? The idea being that if our node seems to 
be kicking /everybody /off the roster maybe there is something wrong 
with the protections.

It would be nice if the node sent a message to the banned peer with a 
code indicating the reason for the ban, specifically the offense that 
put Bitcoin over the edge. Logging the reason is probably fine for most 
cases, but I wanted to put the idea out there, because it might make 
debugging easier if there are some weird bans happening in the wild and 
we can't figure out why.

Should sending lots of messages that don't pass the protocol-level 
checksum test be a bannable offense? Or generally sending garbage data? 
The attacks I'm thinking of are cross-protocol attacks. So as rough 
example: The attacker puts an iframe on a website with a url like 
http://victim.com:8333 so lots of people's browsers connect to it. Maybe 
he could even use something like [magic-bytes]tx\0[...][valid orphan 
transaction] in the URL, so the browser would send GET /[magic-bytes] 
etc. and the Bitcoin node would interpret it.

kjj wrote:

> A few non-standard transactions are probably legitimate.  A whole bunch
> of them are probably not.  I would think that assigning a point or two
> of badness to a peer sending one is pretty reasonable, with the
> understanding that we would need to adjust that as the network evolves.

Strongly disagree. What is a non-standard transaction today may /be /a 
standard transaction tomorrow.


On 9/15/2011 2:25 PM, Gavin Andresen wrote:
> Thanks Mike, that's exactly the kind of detailed review I was looking
> for.  I think you're right an all points.
>
> I'll simplify:  I'll add a -banscore option (default 100), and if a
> node accumulates more than -banscore misbehavior points it'll get
> dropped and banned for -bantime (default 60*60*24) seconds.
>
> I'll make bad signatures a banning offense, and I'll remove the
> number-of-sigops and non-standard-transaction penalties.
>
> I used a mutable field with const setter to avoid modifying a bunch of
> methods to take non-const blocks/transactions instead of const; I
> think it is appropriate because a block/transaction's DoS score is
> really meta-data and not part of it's state.
>
> I'll make GetTime() unit-test friendly as you suggest.
>


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    A few thoughts:<br>
    <br>
    Should the DoS protection auto-disable if the node has less than a
    minimum number of connections? The idea being that if our node seems
    to be kicking <i>everybody </i>off the roster maybe there is
    something wrong with the protections.<br>
    <br>
    It would be nice if the node sent a message to the banned peer with
    a code indicating the reason for the ban, specifically the offense
    that put Bitcoin over the edge. Logging the reason is probably fine
    for most cases, but I wanted to put the idea out there, because it
    might make debugging easier if there are some weird bans happening
    in the wild and we can't figure out why.<br>
    <br>
    Should sending lots of messages that don't pass the protocol-level
    checksum test be a bannable offense? Or generally sending garbage
    data? The attacks I'm thinking of are cross-protocol attacks. So as
    rough example: The attacker puts an iframe on a website with a url
    like <a class="moz-txt-link-freetext" href="http://victim.com:8333">http://victim.com:8333</a> so lots of people's browsers connect to
    it. Maybe he could even use something like
    [magic-bytes]tx\0[...][valid orphan transaction] in the URL, so the
    browser would send GET /[magic-bytes] etc. and the Bitcoin node
    would interpret it.<br>
    <br>
    kjj wrote:<br>
    <br>
    <blockquote type="cite">
      <pre wrap="">A few non-standard transactions are probably legitimate.  A whole bunch 
of them are probably not.  I would think that assigning a point or two 
of badness to a peer sending one is pretty reasonable, with the 
understanding that we would need to adjust that as the network evolves.</pre>
    </blockquote>
    <br>
    Strongly disagree. What is a non-standard transaction today may <i>be
    </i>a standard transaction tomorrow.<br>
    <br>
    <br>
    On 9/15/2011 2:25 PM, Gavin Andresen wrote:
    <blockquote
cite="mid:CABsx9T0Eowp6_mTcggCz3tivRL0NsqyyxqingmPzZ2qkJnU9EA@mail.gmail.com"
      type="cite">
      <pre wrap="">Thanks Mike, that's exactly the kind of detailed review I was looking
for.  I think you're right an all points.

I'll simplify:  I'll add a -banscore option (default 100), and if a
node accumulates more than -banscore misbehavior points it'll get
dropped and banned for -bantime (default 60*60*24) seconds.

I'll make bad signatures a banning offense, and I'll remove the
number-of-sigops and non-standard-transaction penalties.

I used a mutable field with const setter to avoid modifying a bunch of
methods to take non-const blocks/transactions instead of const; I
think it is appropriate because a block/transaction's DoS score is
really meta-data and not part of it's state.

I'll make GetTime() unit-test friendly as you suggest.

</pre>
    </blockquote>
    <br>
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