Subject: Re: [PATCH v3 2/2] column: guard against negative padding

From: Junio C Hamano <[email-masked]>
Date: Tue, 13 Feb 2024 09:06:46 -0800

Kristoffer Haugsbakk <[email-masked]> writes:

> Make sure that client code can’t pass in a negative padding by accident.
>
> Suggested-by: Rubén Justo <[email-masked]>
> Signed-off-by: Kristoffer Haugsbakk <[email-masked]>
> ---
>
> Notes (series):
>     Apparently these are the only publicly-visible functions that use this
>     struct according to `column.h`.
>
>  column.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/column.c b/column.c
> index ff2f0abf399..50bbccc92ee 100644
> --- a/column.c
> +++ b/column.c
> @@ -182,6 +182,8 @@ void print_columns(const struct string_list *list, unsigned int colopts,
>  {
>  	struct column_options nopts;
>  
> +	if (opts && (0 > opts->padding))
> +		BUG("padding must be non-negative");

The only two current callers may happen to be "git branch" that
passes NULL as opts, and "git clean" that passes 2 in opts->padding,
so this BUG() will not trigger.  Once we add new callers to this
function, or update the current callers, this safety start to matter.

The actual breakage from a negative padding happens in layout(),
so another option would be to have this guard there, which will
protect us from having new callers of that function as well, or
its caller display_table(), but these have only one caller each,
so having the guard print_columns() here, that is the closest to
the callers would be fine.

>  	if (!list->nr)
>  		return;
>  	assert((colopts & COL_ENABLE_MASK) != COL_AUTO);
> @@ -361,6 +363,8 @@ int run_column_filter(int colopts, const struct column_options *opts)
>  {
>  	struct strvec *argv;
>  
> +	if (opts && (0 > opts->padding))
> +		BUG("padding must be non-negative");

This one happens to be safe currently because "git tag" passes 2 in
opts->padding, but I do not think this is needed.

We will pass these through to "git column" and the negative padding
will be caught as an error there anyway, no?  So whether "git tag"
is updated or a new caller of run_column_filter() is added, the
developer will already notice it (and they will have to protect
themselves just like the [1/2] of your series did for "git column"
itself).

>  	if (fd_out != -1)
>  		return -1;