list mirror (unofficial, one of many)
 help / color / mirror / code / Atom feed
From: Jeff King <>
To: Constantine <>
Cc: Junio C Hamano <>,
	Christian Couder <>,
	Mike Hommey <>, git <>
Subject: Re: git-clone causes out of memory
Date: Fri, 13 Oct 2017 08:44:56 -0400	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Fri, Oct 13, 2017 at 03:12:43PM +0300, Constantine wrote:

> On 13.10.2017 15:04, Junio C Hamano wrote:
> > Christian Couder <> writes:
> > 
> > > Yeah, but perhaps Git could be smarter when rev-listing too and avoid
> > > processing files or directories it has already seen?
> > 
> > Aren't you suggesting to optimize for a wrong case?
> > 
> Anything that is possible with a software should be considered as a possible
> usecase. It's in fact a DoS attack. Imagine there's a server that using git
> to process something, and now there's a way to knock down this server. It's
> also bad from a promotional stand point.

But the point is that you'd have the same problem with any repository
that had 10^7 files in it. Yes, it's convenient for the attacker that
there are only 9 objects, but fundamentally it's pretty easy for an
attacker to construct repositories that have large trees (or very deep
trees -- that's what causes stack exhaustion in some cases).

Note too that this attack almost always comes down to the diff code
(which is why it kicks in for pathspec limiting) which has to actually
expand the tree. Most "normal" server-side operations (like accepting
pushes or serving fetches) operate only on the object graph and _do_
avoid processing already-seen objects.

As soon as servers start trying to checkout or diff, though, the attack
surface gets quite large. And you really need to start thinking about
having resource limits and quotas for CPU and memory use of each process
(and group by requesting user, IP, repo, etc).

I think the main thing Git could be doing here is to limit the size of
the tree (both width and depth). But arbitrary limits like that have a
way of being annoying, and I think it just pushes resource-exhaustion
attacks off a little (e.g., can you construct a blob that behaves badly
with the "--patch"?).


  reply	other threads:[~2017-10-13 12:45 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-13  9:51 Constantine
2017-10-13 10:06 ` Mike Hommey
2017-10-13 10:26   ` Christian Couder
2017-10-13 10:37     ` Mike Hommey
2017-10-13 10:44       ` Christian Couder
2017-10-13 12:04         ` Junio C Hamano
2017-10-13 12:12           ` Constantine
2017-10-13 12:44             ` Jeff King [this message]
2017-10-13 13:15               ` Derrick Stolee
2017-10-13 13:39                 ` Derrick Stolee
2017-10-13 13:50                   ` Jeff King
2017-10-13 13:55                     ` Derrick Stolee
2017-10-13 13:56                       ` Jeff King
2017-10-13 14:10                         ` Jeff King
2017-10-13 14:20                           ` Jeff King
2017-10-13 14:25                             ` Derrick Stolee
2017-10-13 14:26                               ` Jeff King
2017-10-13 14:30                                 ` Derrick Stolee
2017-10-13 15:27                                 ` [PATCH] revision: quit pruning diff more quickly when possible Jeff King
2017-10-13 15:37                                   ` Derrick Stolee
2017-10-13 15:44                                     ` Jeff King
2017-10-14  2:43                                   ` Junio C Hamano
2017-10-13 12:35   ` git-clone causes out of memory Jeff King

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

  List information:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \
    --subject='Re: git-clone causes out of memory' \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Code repositories for project(s) associated with this inbox:

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).