I've just pushed a whole bunch of commits that I shouldn't have to a bare repo that copies all changed files it receives to our web root using

```
GIT_WORK_TREE=/var/www git checkout -f

```

in a `post-receive` hook.

Because there were a whole load of commits pushed at once, I have no idea what the id was of the previous healthy commit received by the repo.

Is there any way I can undo this push?