Re: [PATCH 1/2] of: fdt: fix memory leak in fdt_ensure_space

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Stefan,

On 31.01.24 17:56, Stefan Kerkmann wrote:
> If the reallocation failed the old memory remains allocated and is never
> freed, this is fixed by freeing the old memory on error.
> 
> Signed-off-by: Stefan Kerkmann <s.kerkmann@pengutronix.de>
> ---
>  drivers/of/fdt.c | 27 ++++++++++++++++++++-------
>  1 file changed, 20 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index 5c21bab5de..4f79a6120f 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -375,24 +375,37 @@ static void *memalign_realloc(void *orig, size_t oldsize, size_t newsize)
>  
>  static int fdt_ensure_space(struct fdt *fdt, int dtsize)
>  {
> +	size_t new_size;
> +	void *previous;
> +
>  	/*
>  	 * We assume strings and names have a maximum length of 1024
>  	 * whereas properties can be longer. We allocate new memory
>  	 * if we have less than 1024 bytes (+ the property size left.
>  	 */
>  	if (fdt->str_size - fdt->str_nextofs < 1024) {
> -		fdt->strings = realloc(fdt->strings, fdt->str_size * 2);
> -		if (!fdt->strings)
> +		previous = fdt->strings;
> +		new_size = fdt->str_size * 2;
> +
> +		if ((fdt->strings = realloc(previous, new_size)) == NULL) {

IMO, it's less readable this way. I'd prefer we leave the realloc line and
then !fdt->strings check on separate lines as before.

> +			free(previous);

This could happen later in the callers (look for out_free) if one wouldn't
set fdt->strings to NULL on error. I don't feel strongly either way, so doing
it this way is fine too.

Change looks good otherwise, so with first comment addressed:

Reviewed-by: Ahmad Fatoum <a.fatoum@pengutronix.de>

Cheers,
Ahmad

>  			return -ENOMEM;
> -		fdt->str_size *= 2;
> +		}
> +
> +		fdt->str_size = new_size;
>  	}
>  
>  	if (fdt->dt_size - fdt->dt_nextofs < 1024 + dtsize) {
> -		fdt->dt = memalign_realloc(fdt->dt, fdt->dt_size,
> -				fdt->dt_size * 2);
> -		if (!fdt->dt)
> +		previous = fdt->dt;
> +		new_size = fdt->dt_size * 2;
> +
> +		if ((fdt->dt = memalign_realloc(previous, fdt->dt_size,
> +						new_size)) == NULL) {
> +			free(previous);
>  			return -ENOMEM;
> -		fdt->dt_size *= 2;
> +		}
> +
> +		fdt->dt_size = new_size;
>  	}
>  
>  	return 0;
> 

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