Re: [PATCH v4 4/6] list-objects: filter objects in traverse_commit_list

[Jeff Hostetler <git@jeffhostetler.com>]

On 11/16/2017 9:14 PM, Junio C Hamano wrote:
> Jeff King <peff@peff.net> writes:
> 
>> Those encodings don't necessarily need to be the same, because they're
>> about transport. Inside each process we'd have the raw bytes, and encode
>> them as appropriate to whatever sub-program we're going to pass to (or
>> not at all if we skip the shell for sub-processes, which is usually a
>> good idea).
> 
> Yes, I share the same feeling.  It does not help that the series
> defines its own notion of arg_needs_armor() and uses it to set a
> field called requires_armor that is not yet used, the definition of
> "armor"ing being each byte getting encoded as two hexadecimal digits
> without any sign (which makes me wonder what a receiver of
> "deadbeef" would do---did it receive an armored string or a plain
> one???).  I do not understand why these strings are not passed as
> opaque sequences of bytes and instead converted at this low a layer.

I'm probably being too paranoid.  My fear is that a client could pass
an expression to clone/fetch/fetch-pack that would be sent to the
server and evaluated by the interface between upload-pack and pack-objects.
I'm not worried about the pack-protocol transport.  I'm mainly concerned
in how upload-pack passes that *client-expression* to pack-objects and are
there ways for that to go south on the server with a carefully crafted
expression.

Even if we assume that upload-pack on the server directly invokes
pack-objects (rather than a shell), there still might be issues.
For platforms like Linux which have a native execve() and can pass
args in an argv (and which the sub-process also receives in an argv
in their main()), my paranoia is probably overkill.

But on Windows, where the native interface takes a command-line string
rather than an argv, I was concerned.  Yes, there is code in compat/mingw.c
to quote args when building a command line from an argv (and I'm *not*
saying there are bugs in that), but again maybe I am being paranoid.

I'll take another look and the existing quoting mechanisms and re-eval.

Thanks,
Jeff