Subject: Re: [PATCH 1/1] attr: add builtin objectmode values support

From: Junio C Hamano <[email-masked]>
Date: Wed, 20 Dec 2023 12:07:12 -0800

Junio C Hamano <[email-masked]> writes:

> The attached is one possible way to plug the leak; I am not sure if
> it is the best one, though.  One thing I like about the solution is
> that the approach makes sure that the mode attributes we would ever
> return are very tightly controlled and does not allow a buggy code
> to come up with "mode" to be passed to this new helper function to
> pass random and unsupported mode bits without triggering the BUG().
>
>  attr.c | 30 +++++++++++++++++++++++++++---
>  1 file changed, 27 insertions(+), 3 deletions(-)

Anybody who want to propose a better leakfix (we cannot afford to do
with UNLEAK() as the number of leaked mode string will be unbounded)?

Otherwise, I'll squash it in to Jonanna's patch and merge it down to
'next'.

Thanks.

> diff --git c/attr.c w/attr.c
> index b03c20f768..679e42258c 100644
> --- c/attr.c
> +++ w/attr.c
> @@ -1250,10 +1250,34 @@ static struct object_id *default_attr_source(void)
>  	return &attr_source;
>  }
>  
> +static const char *interned_mode_string(unsigned int mode)
> +{
> +	static struct {
> +		unsigned int val;
> +		char str[7];
> +	} mode_string[] = {
> +		{ .val = 0040000 },
> +		{ .val = 0100644 },
> +		{ .val = 0100755 },
> +		{ .val = 0120000 },
> +		{ .val = 0160000 },
> +	};
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(mode_string); i++) {
> +		if (mode_string[i].val != mode)
> +			continue;
> +		if (!*mode_string[i].str)
> +			snprintf(mode_string[i].str, sizeof(mode_string[i].str),
> +				 "%06o", mode);
> +		return mode_string[i].str;
> +	}
> +	BUG("Unsupported mode 0%o", mode);
> +}
> +
>  static const char *builtin_object_mode_attr(struct index_state *istate, const char *path)
>  {
>  	unsigned int mode;
> -	struct strbuf sb = STRBUF_INIT;
>  
>  	if (direction == GIT_ATTR_CHECKIN) {
>  		struct object_id oid;
> @@ -1287,8 +1311,8 @@ static const char *builtin_object_mode_attr(struct index_state *istate, const ch
>  		else
>  			return ATTR__UNSET;
>  	}
> -	strbuf_addf(&sb, "%06o", mode);
> -	return strbuf_detach(&sb, NULL);
> +
> +	return interned_mode_string(mode);
>  }
>  
>