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

[Phillip Wood <phillip.wood123@gmail.com>]

Hi Antti

On 11/08/2020 14:13, Antti Keränen wrote:
> '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.
> Fix by duplicating the string before usage, so subsequent calls to
> 'find_unique_abbrev' or other functions calling 'hash_to_hex_algop_r'
> can't overwrite the buffer.
> 
> Found-by: Jussi Keränen <jussike@gmail.com>
> Signed-off-by: Antti Keränen <detegr@rbx.email>

Thanks for working on this

> ---
>   sequencer.c                   |  7 ++++---
>   t/t3404-rebase-interactive.sh | 13 +++++++++++++
>   2 files changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/sequencer.c b/sequencer.c
> index fd7701c88a..0679adb639 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -5178,13 +5178,12 @@ 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();
> +	const char *todo_file = rebase_path_todo();

I'm not sure it's worth rearranging these lines. It probably does not 
matter but we could do

+	char shortonto[GIT_MAX_HEXSZ + 1];

and then later call find_unique_abbrev_r() instead so we don't have to 
worry about freeing shortonto.

>   	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);
> +	char *shortonto;
>   
>   	if (buf->len == 0) {
>   		struct todo_item *item = append_new_todo(todo_list);
> @@ -5206,8 +5205,10 @@ int complete_action(struct repository *r, struct replay_opts *opts, unsigned fla
>   		return error(_("nothing to do"));
>   	}
>   
> +	shortonto = xstrdup(find_unique_abbrev(&oid, DEFAULT_ABBREV));
>   	res = edit_todo_list(r, todo_list, &new_todo, shortrevisions,
>   			     shortonto, flags);
> +	free(shortonto);
>   	if (res == -1)
>   		return -1;
>   	else if (res == -2) {
> diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
> index 4a7d21f898..09af16753c 100755
> --- a/t/t3404-rebase-interactive.sh
> +++ b/t/t3404-rebase-interactive.sh
> @@ -1760,6 +1760,19 @@ 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' '
> +	write_script dump-raw.sh <<-\EOF &&
> +		cat "$1"
> +	EOF
> +	git checkout branch1 &&
> +	(
> +		test_set_editor "$(pwd)/dump-raw.sh" &&
> +		git rebase -i HEAD~5 >actual
> +	) &&

Thanks for taking the trouble to add a test, I think all the lines above 
could be simplified to

	GIT_SEQUENCE_EDITOR=cat git rebase -i HEAD~5 branch1 >actual

> +	onto=$(git rev-parse --short HEAD~5) &&
> +	test_i18ngrep "^# Rebase ..* onto $onto .*" actual

we could lose the final .*

Many Thanks and Best Wishes

Phillip

> +'
> +
>   # This must be the last test in this file
>   test_expect_success '$EDITOR and friends are unchanged' '
>   	test_editor_unchanged
>