[PATCH] xrow: fix request_str crash on long requests

[Vladimir Davydov]

On Mon, Mar 18, 2019 at 07:45:29PM +0300, Vladimir Davydov wrote:
> If tt_static_buf is too small to store the request string, 'pos' will
> become greater than 'end', leading to snprintf(pos, end - pos) crash, as
> it doesn't allow the buffer size to be negative. Use SNPRINT instead.
> ---
> https://github.com/tarantool/tarantool/tree/dv/fix-request-str-crash-on-long-requests
> 
>  src/box/xrow.c            | 33 ++++++++++++++++++++-------------
>  test/box-tap/cfg.test.lua | 21 ++++++++++++++++++++-
>  2 files changed, 40 insertions(+), 14 deletions(-)
> 
> diff --git a/src/box/xrow.c b/src/box/xrow.c
> index bddae1d5..4a0632fe 100644
> --- a/src/box/xrow.c
> +++ b/src/box/xrow.c
> @@ -675,13 +675,11 @@ done:
>  	return 0;
>  }
>  
> -const char *
> -request_str(const struct request *request)
> +static int
> +request_snprint(char *buf, int size, const struct request *request)
>  {
> -	char *buf = tt_static_buf();
> -	char *end = buf + TT_STATIC_BUF_LEN;
> -	char *pos = buf;
> -	pos += snprintf(pos, end - pos, "{type: '%s', "
> +	int total = 0;
> +	SNPRINT(total, snprintf, buf, size, "{type: '%s', "
>  			"replica_id: %u, lsn: %lld, "
>  			"space_id: %u, index_id: %u",
>  			iproto_type_name(request->type),
> @@ -690,18 +688,27 @@ request_str(const struct request *request)
>  			(unsigned) request->space_id,
>  			(unsigned) request->index_id);
>  	if (request->key != NULL) {
> -		pos += snprintf(pos, end - pos, ", key: ");
> -		pos += mp_snprint(pos, end - pos, request->key);
> +		SNPRINT(total, snprintf, buf, size, ", key:");

Oops, skipped ' '.

> +		SNPRINT(total, mp_snprint, buf, size, request->key);
>  	}
>  	if (request->tuple != NULL) {
> -		pos += snprintf(pos, end - pos, ", tuple: ");
> -		pos += mp_snprint(pos, end - pos, request->tuple);
> +		SNPRINT(total, snprintf, buf, size, ", tuple");

Lost the colon (:), sorry.

Amended on the branch.

> +		SNPRINT(total, mp_snprint, buf, size, request->tuple);
>  	}
>  	if (request->ops != NULL) {
> -		pos += snprintf(pos, end - pos, ", ops: ");
> -		pos += mp_snprint(pos, end - pos, request->ops);
> +		SNPRINT(total, snprintf, buf, size, ", ops: ");
> +		SNPRINT(total, mp_snprint, buf, size, request->ops);
>  	}
> -	pos += snprintf(pos, end - pos, "}");
> +	SNPRINT(total, snprintf, buf, size, "}");
> +	return total;
> +}
> +
> +const char *
> +request_str(const struct request *request)
> +{
> +	char *buf = tt_static_buf();
> +	if (request_snprint(buf, TT_STATIC_BUF_LEN, request) < 0)
> +		return "<failed to format request>";
>  	return buf;
>  }