Re: [PATCH 0/3] --end-of-options marker

From: Jeff King <peff@peff.net>
Date: Aug 6, 2019, 23:43 UTC
Message-ID: <20190806234319.GA19178@sigill.intra.peff.net>
In-Reply-To: <20190806225853.GH118825@genre.crustytoothpaste.net>

On Tue, Aug 06, 2019 at 10:58:53PM +0000, brian m. carlson wrote:

Show 19 quoted lines

> On 2019-08-06 at 14:38:30, Jeff King wrote:
> > It's hard for scripted uses of rev-list, etc, to avoid option injection
> > from untrusted arguments, because revision arguments must come before
> > any "--" separator. I.e.:
> > 
> >   git rev-list "$revision" -- "$path"
> > 
> > might mistake "$revision" for an option (with rev-list, that would make
> > it an error, but something like git-log would default to HEAD).
> > 
> > This series provides an alternative to "--" to stop option parsing
> > without indicating that further arguments are pathspecs.
> 
> Sorry, I hadn't had a chance to look at this series in depth, but I was
> wondering: could we not just accept two separate "--" arguments, and if
> there are two of them, interpret the first with the traditional meaning
> and the second with the Git-specific meaning? That would be much more
> intuitive for folks, although I suspect it would take a little more work
> in the options parser.

That also crossed my mind, but I think it opens up some complicated corner cases. For instance, if I'm parsing left-to-right and see "--", how do I know which separator it is meant to be? I think the only rule that makes sense is that you must have two "--", like:

  git rev-list [options] -- [revs] -- [paths]

but that means parsing the whole thing before we can interpret any of it. What kinds of tricks can an attacker play by putting "--" in the revs or paths areas? E.g., what does this mean:

  # expanded from "git rev-list -- $revs -- $paths"
  git rev-list -- --foo -- -- --bar --

I think if we at least choose the left-most "--" as the official end-of-options then they can't inject an option (they can only inject a rev as a path). I guess that's the same as with --end-of-options. But it somehow feels less clear to me than a separate marker.

It also doesn't allow this:

  # allow paths and revs, with optional separator, but no more options
  git rev-list --end-of-options "$@"

though I'm not sure whether anybody cares.

-Peff