Re: [PATCH 1/4] KVM-S390: Improve determination of sizes in kvm_s390_import_bp_data()

walter harms
2016-08-18T07:25:39Z

Am 17.08.2016 20:06, schrieb SF Markus Elfring:
> From: Markus Elfring <elfring@users.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@users.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