Re: [PATCH 0/3] credential: handle partial URLs in config settings again

From: Jonathan Nieder <jrnieder@gmail.com>
Date: Apr 22, 2020, 22:47 UTC
Message-ID: <20200422224711.GC140314@google.com>
In-Reply-To: <nycvar.QRO.7.76.6.2004230019170.18039@tvgsbejvaqbjf.bet>

Hi,

Johannes Schindelin wrote:

> On Wed, 22 Apr 2020, Jeff King wrote:
>> On Wed, Apr 22, 2020 at 08:51:02PM +0000, Johannes Schindelin via GitGitGadget wrote:

Show 20 quoted lines

>>> Please note that Git v2.17.4 will not do what we would expect here: if any
>>> host name (without protocol) is specified, e.g. -c
>>> credential.golli.wog.username = boo, it will actually ignore the host name.
>>> That is, this will populate the username:
>>>
>>>   $ echo url=https://example.com |
>>>     git -c credential.totally.bog.us.username=foo credential fill
>>
>> That seems scary. What if it is not .username, but:
>>
>>   [credential "example.com"]
>>   username = foo
>>   helper = "!echo password=bar"
>>
>> ? (Or you can imagine a helper that is pulling from a read-only store,
>> like "pass"). That would send the credential to the wrong host.
>
> It would. But I am not aware of any implications regarding `.gitmodules`
> (for some reason I now expect every bug to open an attack vector via
> submodules, I wonder why that is), so that's at least good.

Submodules are only one of many ways that people end up cloning from an attacker-controlled URL. In submodules we're careful not to use --recurse-submodules by default at clone time. So I'll mentally subsitute "attacker-controlled URLs" where you say "submodules". ;-)

I agree with Peff's concern about the unpatched state: since there are people who use `[credential "host.example.com"] helper` and there are credential helpers that ignore the host passed in, the combination can hurt people. (Fortunately, there aren't many credential helpers in that category that are commonly used.)

[...]

> Yes. For the record, I tried to be very careful here. The _only_ code path
> that is affected by this change is the config reading.

[...]

> But again, I would love another pair of eyes on this, to confirm my
> analysis.

As mentioned above, the config reading is sensitive, too. That said, I suspect you got it to do basically the right thing.

Reading through the patches.  Thank you.

Jonathan