linux-kernel - Re: [PATCH 1/4] KVM-S390: Improve determination of sizes in kvm_s390_import_bp

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Message-ID: <57B562F3.1080004@bfs.de>
Date:	Thu, 18 Aug 2016 09:25:39 +0200
From:	walter harms <wharms@....de>
To:	SF Markus Elfring <elfring@...rs.sourceforge.net>
CC:	kvm@...r.kernel.org, linux-s390@...r.kernel.org,
	Christian Bornträger 
	<borntraeger@...ibm.com>, Cornelia Huck <cornelia.huck@...ibm.com>,
	David Hildenbrand <dahi@...ux.vnet.ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Radim Krčmář <rkrcmar@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	kernel-janitors@...r.kernel.org,
	Julia Lawall <julia.lawall@...6.fr>
Subject: Re: [PATCH 1/4] KVM-S390: Improve determination of sizes in kvm_s390_import_bp_data()



Am 17.08.2016 20:06, schrieb SF Markus Elfring:
> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Wed, 17 Aug 2016 18:29:04 +0200
> 
> Replace the specification of data structures by pointer dereferences
> to make the corresponding size determination a bit safer according to
> the Linux coding style convention.
> 
> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
>  arch/s390/kvm/guestdbg.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/s390/kvm/guestdbg.c b/arch/s390/kvm/guestdbg.c
> index d1f8241..b68db4b 100644
> --- a/arch/s390/kvm/guestdbg.c
> +++ b/arch/s390/kvm/guestdbg.c
> @@ -216,7 +216,7 @@ int kvm_s390_import_bp_data(struct kvm_vcpu *vcpu,
>  	else if (dbg->arch.nr_hw_bp > MAX_BP_COUNT)
>  		return -EINVAL;
>  
> -	size = dbg->arch.nr_hw_bp * sizeof(struct kvm_hw_breakpoint);
> +	size = dbg->arch.nr_hw_bp * sizeof(*bp_data);
>  	bp_data = kmalloc(size, GFP_KERNEL);
>  	if (!bp_data) {
>  		ret = -ENOMEM;
> @@ -241,7 +241,7 @@ int kvm_s390_import_bp_data(struct kvm_vcpu *vcpu,
>  		}
>  	}
>  
> -	size = nr_wp * sizeof(struct kvm_hw_wp_info_arch);
> +	size = nr_wp * sizeof(*wp_info);
>  	if (size > 0) {
>  		wp_info = kmalloc(size, GFP_KERNEL);
>  		if (!wp_info) {
> @@ -249,7 +249,7 @@ int kvm_s390_import_bp_data(struct kvm_vcpu *vcpu,
>  			goto error;
>  		}
>  	}
> -	size = nr_bp * sizeof(struct kvm_hw_bp_info_arch);
> +	size = nr_bp * sizeof(*bp_info);
>  	if (size > 0) {
>  		bp_info = kmalloc(size, GFP_KERNEL);
>  		if (!bp_info) {


IMHO the common pattern for kmalloc is
  bp_info = kmalloc( nr_bp * sizeof(*bp_info), GFP_KERNEL);

i can not remember code with a check for size < 0, i guess it is here
to avoid an overflow ? since kmalloc takes a size_t argument this would cause
a malloc failure an can be ignored.


just my 2 cents.
re,
 wh