Re: [PATCH] s390/pkey: prevent overflow in size calculation for memdup_user()

[Heiko Carstens <hca@linux.ibm.com>]

On Wed, Jun 11, 2025 at 08:21:15PM +0300, Fedor Pchelkin wrote:
> Number of apqn target list entries contained in 'nr_apqns' variable is
> determined by userspace via an ioctl call so the result of the product in
> calculation of size passed to memdup_user() may overflow.
> 
> In this case the actual size of the allocated area and the value
> describing it won't be in sync leading to various types of unpredictable
> behaviour later.
> 
> Return an error if an overflow is detected. Note that it is different
> from when nr_apqns is zero - that case is considered valid and should be
> handled in subsequent pkey_handler implementations.
> 
> Found by Linux Verification Center (linuxtesting.org).
> 
> Fixes: f2bbc96e7cfa ("s390/pkey: add CCA AES cipher key support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
> ---
>  drivers/s390/crypto/pkey_api.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/s390/crypto/pkey_api.c b/drivers/s390/crypto/pkey_api.c
> index cef60770f68b..a731fc9c62a7 100644
> --- a/drivers/s390/crypto/pkey_api.c
> +++ b/drivers/s390/crypto/pkey_api.c
> @@ -83,10 +83,15 @@ static void *_copy_key_from_user(void __user *ukey, size_t keylen)
>  
>  static void *_copy_apqns_from_user(void __user *uapqns, size_t nr_apqns)
>  {
> +	size_t size;
> +
>  	if (!uapqns || nr_apqns == 0)
>  		return NULL;
>  
> -	return memdup_user(uapqns, nr_apqns * sizeof(struct pkey_apqn));
> +	if (check_mul_overflow(nr_apqns, sizeof(struct pkey_apqn), &size))
> +		return ERR_PTR(-EINVAL);
> +
> +	return memdup_user(uapqns, size);

Thanks! Is there any specific reason why this is open-coding
memdup_array_user()?

If not, please send a new version which does the simple conversion.