Re: [PATCH] s390/pkey: Use memdup_user() rather than duplicating its implementation

Joe Perches
2019-11-06T10:38:39Z

On Wed, 2019-11-06 at 11:22 +0100, Markus Elfring wrote:
> From: Markus Elfring <elfring@users.sourceforge.net>
> Date: Wed, 6 Nov 2019 11:11:42 +0100
>
> Reuse existing functionality from memdup_user() instead of keeping
> duplicate source code.
>
> Generated by: scripts/coccinelle/api/memdup_user.cocci
>
> Delete local variables which became unnecessary with this refactoring
> in two function implementations.
>
> Fixes: f2bbc96e7cfad3891b7bf9bd3e566b9b7ab4553d ("s390/pkey: add CCA AES cipher key support")

This doesn't fix anything and the Fixes: line is not appropriate.

> diff --git a/drivers/s390/crypto/pkey_api.c b/drivers/s390/crypto/pkey_api.c
[]
> @@ -715,36 +715,16 @@ static int pkey_apqns4keytype(enum pkey_key_type ktype,
>
> static void *_copy_key_from_user(void __user *ukey, size_t keylen)
> {
> - void *kkey;
> -
> - if (!ukey || keylen < MINKEYBLOBSIZE || keylen > KEYBLOBBUFSIZE)
> - return ERR_PTR(-EINVAL);
> - kkey = kmalloc(keylen, GFP_KERNEL);
> - if (!kkey)
> - return ERR_PTR(-ENOMEM);
> - if (copy_from_user(kkey, ukey, keylen)) {
> - kfree(kkey);
> - return ERR_PTR(-EFAULT);
> - }
> -
> - return kkey;
> + return !ukey || keylen < MINKEYBLOBSIZE || keylen > KEYBLOBBUFSIZE
> + ? ERR_PTR(-EINVAL)
> + : memdup_user(ukey, keylen);

This is a very poor use of ternary ?: code.
This is much more readable for humans.

if (!ukey || keylen < MINKEYBLOBSIZE || keylen > KBLOBBUFSIZE)
return ERR_PTR(-EINVAL);

return memdup_user(ukey, keylen);

The compiler will produce the same code.

> static void *_copy_apqns_from_user(void __user *uapqns, size_t nr_apqns)
> {
> - void *kapqns = NULL;
> - size_t nbytes;
> -
> - if (uapqns && nr_apqns > 0) {
> - nbytes = nr_apqns * sizeof(struct pkey_apqn);
> - kapqns = kmalloc(nbytes, GFP_KERNEL);
> - if (!kapqns)
> - return ERR_PTR(-ENOMEM);
> - if (copy_from_user(kapqns, uapqns, nbytes))
> - return ERR_PTR(-EFAULT);
> - }
> -
> - return kapqns;
> + return uapqns && nr_apqns > 0
> + ? memdup_user(uapqns, nr_apqns * sizeof(struct pkey_apqn))
> + : NULL;

And here you reverse the form of the earlier block.
Please be consistent and use this style:

if (!uapqns || nr_apqns <= 0)
return NULL;

return memdup_user(uapqns, nr_apqns * sizeof(struct pkey_apqn));