On Sat, Oct 20, 2018 at 02:58:53PM -0400, Jeff King wrote:
> On Sat, Oct 20, 2018 at 01:14:28PM +0200, Ævar Arnfjörð Bjarmason wrote:
>
> > > I'd guess this sort of thing is pretty rare. But I wonder if we're
> > > crossing the line of trying to assume too much about what the user's
> > > arbitrary code does.
> > >
> > > A simple depth counter can limit the fork bomb, and with a high enough
> > > depth would be unlikely to trigger a false positive. It could also
> > > protect non-aliases more reasonably, too (e.g., if you have a 1000-deep
> > > git process hierarchy, there's a good chance you've found an infinite
> > > loop in git itself).
> >
> > I don't think this edge case you're describing is very plausible, and I
> > doubt it exists in the wild.
> >
> > But going by my personal incredulity and a git release breaking code in
> > the wild would suck, so agree that I need to re-roll this to anticipate
> > that.
>
> I agree it's probably quite rare, if it exists at all. But I also wonder
> how important looping alias protection is. It's also rare, and the
> outcome is usually "gee, I wonder why this is taking so long? ^C".
Hmph. So I was speaking before purely hypothetically, but now that your
patch is in 'next', it is part of my daily build. And indeed, I hit a
false positive within 5 minutes of building it. ;)
I have an alias like this:
$ git help dotgit
'dotgit' is aliased to '!git rev-parse 2>/dev/null || cd ~/compile/git; git'
The idea being that I can run "git dotgit foo" to run "git foo" in the
current directory, or if it is not a git repository, in my checkout of
git.git.
I use it in two ways:
- some of my aliases know about it themselves. So I have an alias "ll"
that does:
$ git help ll
'll' is aliased to '!git dotgit --no-pager log --no-walk=unsorted
--format='%h (%s, %ad)' --date=short'
with the idea being to produce a nice annotation for a commit id.
Using "git dotgit" there lets me just run it from any directory,
since 99% of the time I am working on git.git anyway.
- I have a vim command defined:
command! -nargs=* Git :call MaybeInlineCommand("git dotgit <args>")
so I can do ":Git foo" inside vim and it uses either the current
repo (e.g., if I'm writing a commit message) or git.git (e.g., if
I'm writing an email and didn't start in the repo).
So of course the alias expansion is something like (in older versions of
Git):
1. "git dotgit ll" runs the dotgit alias, which sees that we need to go
to the git.git checkout
2. that runs "git ll"
3. that runs "git dotgit log"; this second dotgit invocation sees we're
already in a repository and is a noop
4. git-log runs
With your patch, step 3 complains:
$ git dotgit ll
fatal: alias loop detected: expansion of 'dotgit' does not terminate:
dotgit <==
ll ==>
So I would really prefer a depth counter that can be set sufficiently
high to make this case work. ;)
As an aside, I got to experience this error message as an unsuspecting
user would. Unfortunately the output was not super helpful for figuring
out the cause. I scratched my head for a while before remembering that
"ll" uses "dotgit" explicitly (which was quite apparent when running
GIT_TRACE=1, or "git help ll"). I think showing the alias definitions in
the loop output would have made it much more obvious (if perhaps a bit
uglier). E.g., something like:
fatal: alias loop...
==> dotgit is aliased to '!git rev-parse ...'
<== ll is aliased to '!git dotgit ...'
-Peff
