Re: [PATCH][next] openprom: Use struct_size() helper

Kees Cook
2023-06-29T20:04:06Z

On Thu, Jun 22, 2023 at 05:25:13PM -0600, Gustavo A. R. Silva wrote:
> Prefer struct_size() over open-coded versions.

This commit log could be more descriptive since the replacement below
isn't in the standard "sizeof(struct) + sizeof(element) * count" format.
:) It took me a moment to figure out what was going on:

struct openpromio
{
unsigned int oprom_size; /* Actual size of the oprom_array. */
char oprom_array[]; /* Holds property names and values. */
};

sizeof(struct openpromio) == sizeof(int) :P

>
> Link: https://github.com/KSPP/linux/issues/160
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
> drivers/sbus/char/openprom.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/sbus/char/openprom.c b/drivers/sbus/char/openprom.c
> index 30b9751aad30..de56c8fec373 100644
> --- a/drivers/sbus/char/openprom.c
> +++ b/drivers/sbus/char/openprom.c
> @@ -76,7 +76,9 @@ static int copyin(struct openpromio __user *info, struct openpromio **opp_p)
> if (bufsize > OPROMMAXPARAM)
> bufsize = OPROMMAXPARAM;
>
> - if (!(*opp_p = kzalloc(sizeof(int) + bufsize + 1, GFP_KERNEL)))
> + *opp_p = kzalloc(struct_size(*opp_p, oprom_array, bufsize + 1),
> + GFP_KERNEL);
> + if (!*opp_p)
> return -ENOMEM;
>
> if (copy_from_user(&(*opp_p)->oprom_array,
> @@ -95,7 +97,9 @@ static int getstrings(struct openpromio __user *info, struct openpromio **opp_p)
> if (!info || !opp_p)
> return -EFAULT;
>
> - if (!(*opp_p = kzalloc(sizeof(int) + OPROMMAXPARAM + 1, GFP_KERNEL)))
> + *opp_p = kzalloc(struct_size(*opp_p, oprom_array, OPROMMAXPARAM + 1),
> + GFP_KERNEL);
> + if (!*opp_p)
> return -ENOMEM;

With that understood, yeah, these look good to me. :)

Reviewed-by: Kees Cook <keescook@chromium.org>

--
Kees Cook