Re: [PATCH v2] rebase -i: Fix possibly wrong onto hash in todo

> 'todo_list_write_to_file' may overwrite the static buffer, originating
> from 'find_unique_abbrev', that was used to store the short commit hash
> 'c' for "# Rebase a..b onto c" message in the todo editor. This is
> because the buffer that is returned from 'find_unique_abbrev' is valid
> until 4 more calls to `find_unique_abbrev` are made.
> 
> As 'todo_list_write_to_file' calls 'find_unique_abbrev' for each rebased
> commit, the hash for 'c' is overwritten if there are 4 or more commits
> in the rebase. This behavior has been broken since its introduction.
> 
> Fix by storing the short onto commit hash in a different buffer that
> remains valid, before calling 'todo_list_write_to_file'.
> 
> Found-by: Jussi Keränen <jussike@gmail.com>
> Signed-off-by: Antti Keränen <detegr@rbx.email>
> ---
>  sequencer.c                   | 5 +++--
>  t/t3404-rebase-interactive.sh | 6 ++++++
>  2 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/sequencer.c b/sequencer.c
> index fd7701c88a..e2007dbb8c 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -5178,13 +5178,14 @@ int complete_action(struct repository *r, struct replay_opts *opts, unsigned fla
>  		    struct string_list *commands, unsigned autosquash,
>  		    struct todo_list *todo_list)
>  {
> -	const char *shortonto, *todo_file = rebase_path_todo();
> +	char shortonto[GIT_MAX_HEXSZ + 1];
> +	const char *todo_file = rebase_path_todo();
>  	struct todo_list new_todo = TODO_LIST_INIT;
>  	struct strbuf *buf = &todo_list->buf, buf2 = STRBUF_INIT;
>  	struct object_id oid = onto->object.oid;
>  	int res;
>  
> -	shortonto = find_unique_abbrev(&oid, DEFAULT_ABBREV);
> +	find_unique_abbrev_r(shortonto, &oid, DEFAULT_ABBREV);
>  
>  	if (buf->len == 0) {
>  		struct todo_item *item = append_new_todo(todo_list);
> diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
> index 4a7d21f898..1b4fa0843e 100755
> --- a/t/t3404-rebase-interactive.sh
> +++ b/t/t3404-rebase-interactive.sh
> @@ -1760,6 +1760,12 @@ test_expect_success 'correct error message for commit --amend after empty pick'
>  	test_i18ngrep "middle of a rebase -- cannot amend." err
>  '
>  
> +test_expect_success 'todo has correct onto hash' '
> +	GIT_SEQUENCE_EDITOR=cat git rebase -i no-conflict-branch~4 no-conflict-branch >actual &&
> +	onto=$(git rev-parse --short HEAD~4) &&
> +	test_i18ngrep "^# Rebase ..* onto $onto" actual
> +'
> +
>  # This must be the last test in this file
>  test_expect_success '$EDITOR and friends are unchanged' '
>  	test_editor_unchanged
>