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From: Junio C Hamano <>
To: Jonathan Tan <>
Subject: Re: Proposal for missing blob support in Git repos
Date: Mon, 01 May 2017 18:41:27 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <> (Jonathan Tan's message of "Mon, 1 May 2017 17:33:01 -0700")

Jonathan Tan <> writes:

> On 05/01/2017 04:29 PM, Junio C Hamano wrote:
>> Jonathan Tan <> writes:
>>> Thanks for your comments. If you're referring to the codepath
>>> involving write_sha1_file() (for example, builtin/hash-object ->
>>> index_fd or builtin/unpack-objects), that is fine because
>>> write_sha1_file() invokes freshen_packed_object() and
>>> freshen_loose_object() directly to check if the object already exists
>>> (and thus does not invoke the new mechanism in this patch).
>> Is that a good thing, though?  It means that you an attacker can
>> feed one version to the remote object store your "grab blob" hook
>> gets the blobs from, and have you add a colliding object locally,
>> and the usual "are we recording the same object as existing one?"
>> check is bypassed.
> If I understand this correctly, what you mean is the situation where
> the hook adds an object to the local repo, overriding another object
> of the same name?


write_sha1_file() pays attention to objects already in the local
object store to avoid hash collisions that can be used to replace a
known-to-be-good object and that is done as a security measure.
What I am reading in your response was that this new mechanism
bypasses that, and I was wondering if that is a good thing.

  parent reply	other threads:[~2017-05-02  1:41 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-26 22:13 Proposal for missing blob support in Git repos Jonathan Tan
2017-05-01  3:57 ` Junio C Hamano
2017-05-01 19:12   ` Jonathan Tan
2017-05-01 23:29     ` Junio C Hamano
2017-05-02  0:33       ` Jonathan Tan
2017-05-02  0:38         ` Brandon Williams
2017-05-02  1:41         ` Junio C Hamano [this message]
2017-05-02 17:21           ` Jonathan Tan
2017-05-02 18:32             ` Ævar Arnfjörð Bjarmason
2017-05-02 21:45               ` Jonathan Tan
2017-05-04  4:29                 ` Junio C Hamano
2017-05-04 17:09                   ` Jonathan Tan

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