Re: [PATCH alsa-lib 8/8] topology: Make buffer for saving dynamic size

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

On 6/25/20 6:03 AM, Piotr Maziarz wrote:
> Some fields can exceed size limit, e.g. private data has no size
> restriction. Therefore it needs to be dynamically increased.
> 
> Signed-off-by: Piotr Maziarz <piotrx.maziarz@linux.intel.com>
> ---
>   src/topology/save.c | 36 ++++++++++++++++++++++++++++++------
>   1 file changed, 30 insertions(+), 6 deletions(-)
> 
> diff --git a/src/topology/save.c b/src/topology/save.c
> index 4ecf86c..d6ee8b6 100644
> --- a/src/topology/save.c
> +++ b/src/topology/save.c
> @@ -19,22 +19,43 @@
>   #include "tplg_local.h"
>   
>   #define SAVE_ALLOC_SHIFT	(13)	/* 8192 bytes */
> +#define PRINT_BUF_SIZE		(1024)
> +#define PRINT_BUF_SIZE_MAX	(1024 * 1024)
>   
>   int tplg_save_printf(char **dst, const char *pfx, const char *fmt, ...)
>   {
>   	va_list va;
> -	char buf[1024], *s;
> -	size_t n, l, t, pl;
> +	char *buf, *s;
> +	size_t n, alloc_size = PRINT_BUF_SIZE, l, t, pl;
> +	int ret = 0;
> +
> +	buf = malloc(alloc_size);
> +	if (!buf)
> +		return -ENOMEM;
>   
>   	if (pfx == NULL)
>   		pfx = "";
>   
> +again:
>   	va_start(va, fmt);
> -	n = vsnprintf(buf, sizeof(buf), fmt, va);
> +	n = vsnprintf(buf, alloc_size, fmt, va);
>   	va_end(va);
>   
> -	if (n >= sizeof(buf))
> -		return -EOVERFLOW;
> +	if (n >= PRINT_BUF_SIZE_MAX) {
> +		ret = -EOVERFLOW;
> +		goto end;
> +	}

what this patch does is change the allocation limit from 1KB to 1MB, but 
the data still has no size restriction. At what point do we decide to 
throw an error?

> +
> +	if (n >= alloc_size) {
> +		char *tmp = realloc(buf, n + 1);
> +		if (!tmp) {
> +			ret = -ENOMEM;
> +			goto end;
> +		}
> +		buf = tmp;
> +		alloc_size = n + 1;
> +		goto again;
> +	}
>   
>   	pl = strlen(pfx);
>   	l = *dst ? strlen(*dst) : 0;
> @@ -47,7 +68,8 @@ int tplg_save_printf(char **dst, const char *pfx, const char *fmt, ...)
>   		if (s == NULL) {
>   			free(*dst);
>   			*dst = NULL;
> -			return -ENOMEM;
> +			ret = -ENOMEM;
> +			goto end;
>   		}
>   	} else {
>   		s = *dst;
> @@ -57,6 +79,8 @@ int tplg_save_printf(char **dst, const char *pfx, const char *fmt, ...)
>   		strcpy(s + l, pfx);
>   	strcpy(s + l + pl, buf);
>   	*dst = s;
> +end:
> +	free(buf);
>   	return 0;
>   }
>   
>