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

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Message-ID: <6137855bb4170c438c7436cbdb7dfd21639a8855.camel@perches.com>
Date:   Wed, 06 Nov 2019 02:38:39 -0800
From:   Joe Perches <joe@...ches.com>
To:     Markus Elfring <Markus.Elfring@....de>, linux-s390@...r.kernel.org,
        Christian Bornträger <borntraeger@...ibm.com>,
        Harald Freudenberger <freude@...ux.ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Ingo Franzki <ifranzki@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] s390/pkey: Use memdup_user() rather than duplicating
 its implementation

On Wed, 2019-11-06 at 11:22 +0100, Markus Elfring wrote:
> From: Markus Elfring <elfring@...rs.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));