From: Junio C Hamano <gitster@pobox.com>
Date: Mon, 05 Nov 2018 02:10:53 GMT
Subject: Re: [PATCH v2 5/5] pretty: add support for separator option in %(trailers)
Message-ID: <xmqqpnvkjmtu.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <20181104152232.20671-6-anders@0x63.nu>

Anders Waldenborg <anders@0x63.nu> writes:

> @@ -1352,6 +1353,17 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
>  						arg++;
>  
>  					opts.only_trailers = 1;
> +				} else if (skip_prefix(arg, "separator=", &arg)) {
> +					size_t seplen = strcspn(arg, ",)");
> +					strbuf_reset(&sepbuf);
> +					char *fmt = xstrndup(arg, seplen);
> +					strbuf_expand(&sepbuf, fmt, format_fundamental, NULL);

This somehow feels akin to using end-user supplied param to printf(3)
as its format argument e.g.

	int main(int ac, char *av) {
		printf(av[1]);
		return 0;
	}

which is not a good idea.  Is there a mechanism with which we can
ensure that the separator=<what> specification will never come from
potentially malicious sources (e.g. not used to show things on webpage
allowing random folks who access he site to supply custom format)?