Re: Useless error message?

From: Jonathan Nieder <jrnieder@gmail.com>
Date: Apr 22, 2010, 10:15 UTC
Message-ID: <20100422101535.GB625@progeny.tock>
In-Reply-To: <4BD01E09.8080504@op5.se>

Andreas Ericsson wrote:

> On 04/22/2010 11:42 AM, Jonathan Nieder wrote:

Show 7 quoted lines

>> [1] I do suspect that in the case of failing enter_repo() or missing
>> git-daemon-export-ok, saying “cannot read the specified repo” would be
>> fine.  Most of the time, there is not much value in disclosing a more
>> detailed reason, anyway.
>
> That would make it possible for random attackers to determine whether
> a specific user exists on the system, which is very bad indeed.

I guess I am missing something.  How would

(*) $ git clone git://git.example.com/~u/foo
    remote: Cannot read the specified repo

tell me whether that user existed on the system? If the daemon gives the same message for ENOENT, missing git-daemon-export-ok, EPERM, and so on so I cannot distinguish the cases, then I just don’t see the problem.

If the daemon failed for some other reason, like a flaky network, I would see

    $ git clone git://git.example.com/~u/foo
    fatal: The remote end hung up unexpectedly

So the extra information could still be helpful, without unwanted information disclosure. In the case (*) I learn definitively that the address I specified does not represent a repo I have access to, rather than this being some random, transient unexplained problem.

Thanks for the comment. Jonathan