Re: [PATCH 1/6] run_external_diff: use an argv_array for the command line

> We currently generate the command-line for the external
> command using a fixed-length array of size 10. But if there
> is a rename, we actually need 11 elements (10 items, plus a
> NULL), and end up writing a random NULL onto the stack.
>
> Rather than bump the limit, let's just an argv_array, which
> makes this sort of error impossible.
>
> Noticed-by: Max L <infthi.inbox@gmail.com>
> Signed-off-by: Jeff King <peff@peff.net>
> ---
> This was actually noticed by a GitHub user, who proposed bumping
> the array size to 11:
>
>   https://github.com/git/git/pull/92
>
> Even though this fix is a bigger change, I'd rather do it this way, as
> it is more obviously correct to a reader (and it solves the problem
> forever). I pulled the name/email from that commit, but please let me
> know if you'd prefer to be credited differently.
>
>  diff.c | 32 ++++++++++++++++----------------
>  1 file changed, 16 insertions(+), 16 deletions(-)
>
> diff --git a/diff.c b/diff.c
> index 539997f..b154284 100644
> --- a/diff.c
> +++ b/diff.c
> @@ -16,6 +16,7 @@
>  #include "submodule.h"
>  #include "ll-merge.h"
>  #include "string-list.h"
> +#include "argv-array.h"
>
>  #ifdef NO_FAST_WORKING_DIRECTORY
>  #define FAST_WORKING_DIRECTORY 0
> @@ -2902,9 +2903,8 @@ static void run_external_diff(const char *pgm,
>  			      int complete_rewrite,
>  			      struct diff_options *o)
>  {
> -	const char *spawn_arg[10];
> +	struct argv_array argv = ARGV_ARRAY_INIT;
>  	int retval;
> -	const char **arg = &spawn_arg[0];
>  	struct diff_queue_struct *q = &diff_queued_diff;
>  	const char *env[3] = { NULL };
>  	char env_counter[50];
> @@ -2915,23 +2915,22 @@ static void run_external_diff(const char *pgm,
>  		const char *othername = (other ? other : name);
>  		temp_one = prepare_temp_file(name, one);
>  		temp_two = prepare_temp_file(othername, two);
> -		*arg++ = pgm;
> -		*arg++ = name;
> -		*arg++ = temp_one->name;
> -		*arg++ = temp_one->hex;
> -		*arg++ = temp_one->mode;
> -		*arg++ = temp_two->name;
> -		*arg++ = temp_two->hex;
> -		*arg++ = temp_two->mode;
> +		argv_array_push(&argv, pgm);
> +		argv_array_push(&argv, name);
> +		argv_array_push(&argv, temp_one->name);
> +		argv_array_push(&argv, temp_one->hex);
> +		argv_array_push(&argv, temp_one->mode);
> +		argv_array_push(&argv, temp_two->name);
> +		argv_array_push(&argv, temp_two->hex);
> +		argv_array_push(&argv, temp_two->mode);
>  		if (other) {
> -			*arg++ = other;
> -			*arg++ = xfrm_msg;
> +			argv_array_push(&argv, other);
> +			argv_array_push(&argv, xfrm_msg);
>  		}
>  	} else {
> -		*arg++ = pgm;
> -		*arg++ = name;
> +		argv_array_push(&argv, pgm);
> +		argv_array_push(&argv, name);
>  	}
> -	*arg = NULL;
>  	fflush(NULL);
>
>  	env[0] = env_counter;
> @@ -2940,8 +2939,9 @@ static void run_external_diff(const char *pgm,
>  	env[1] = env_total;
>  	snprintf(env_total, sizeof(env_total), "GIT_DIFF_PATH_TOTAL=%d", q->nr);
>
> -	retval = run_command_v_opt_cd_env(spawn_arg, RUN_USING_SHELL, NULL, env);
> +	retval = run_command_v_opt_cd_env(argv.argv, RUN_USING_SHELL, NULL, env);
>  	remove_tempfile();
> +	argv_array_clear(&argv);
>  	if (retval) {
>  		fprintf(stderr, "external diff died, stopping at %s.\n", name);
>  		exit(1);
> --
> 1.9.1.656.ge8a0637
>
>