Re: [PATCH v2] sparse index: fix use-after-free bug in cache_tree_verify()

> From: Phillip Wood <phillip.wood@dunelm.org.uk>
> 
> In a sparse index it is possible for the tree that is being verified
> to be freed while it is being verified. This happens when the index is
> sparse but the cache tree is not and index_name_pos() looks up a path
> from the cache tree that is a descendant of a sparse index entry. That
> triggers a call to ensure_full_index() which frees the cache tree that
> is being verified.  Carrying on trying to verify the tree after this
> results in a use-after-free bug. Instead restart the verification if a
> sparse index is converted to a full index. This bug is triggered by a
> call to reset_head() in "git rebase --apply". Thanks to René Scharfe
> and Derick Stolee for their help analyzing the problem.