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

From: Taylor Blau <me@ttaylorr.com>
Date: Aug 7, 2019, 16:54 UTC
Message-ID: <20190807165431.GA60876@syl.local>
In-Reply-To: <20190807041749.GI118825@genre.crustytoothpaste.net>

On Wed, Aug 07, 2019 at 04:17:49AM +0000, brian m. carlson wrote:

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> On 2019-08-06 at 23:43:20, Jeff King wrote:
> > On Tue, Aug 06, 2019 at 10:58:53PM +0000, brian m. carlson wrote:
> > > 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]
>
> I was assuming that we wouldn't have a huge number of command-line
> arguments and we'd check ahead, although that could of course cause some
> pain when used with xargs, I suppose, especially on Linux with its huge
> ARG_MAX.
>
> > 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.

This is definitely the secure option among the two, but I'm not sure that it makes me feel better about this alternative direction. I dislike the ambiguity in having two '--'s, and I don't think that this is something we ought to concern callers with.

'--end-of-options' is on the one hand, cumbersome to write, but it is clear. I think that this is an acceptable trade-off, because we don't expect users at the command line to ever type this. So, some extra clarity in favor of a drop in convenience for a supposedly smaller number of use cases seems like a favorable trade-off to me.

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> I suppose if there's more than two, then interpret the first one as the
> end-of-options marker, the second one in the traditional way, and any
> subsequent ones as pathspecs matching the file "--". Writing such a
> command line would be silly, but we'd fail secure.
>
> > 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.
>
> That's a good point. I don't have a strong view either way, but I
> thought I'd ask about alternatives.
> --
> brian m. carlson: Houston, Texas, US
> OpenPGP: https://keybase.io/bk2204

Thanks, Taylor