Re: [PATCH 5/6] treewide: use kv[mz]alloc* rather than opencoded variants

[Vlastimil Babka]

On 01/12/2017 06:37 PM, Michal Hocko wrote:
> On Thu 12-01-17 09:26:09, Kees Cook wrote:
>> On Thu, Jan 12, 2017 at 7:37 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> [...]
>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>>> index 4f74511015b8..e6bbb33d2956 100644
>>> --- a/arch/s390/kvm/kvm-s390.c
>>> +++ b/arch/s390/kvm/kvm-s390.c
>>> @@ -1126,10 +1126,7 @@ static long kvm_s390_get_skeys(struct kvm *kvm, struct kvm_s390_skeys *args)
>>>         if (args->count < 1 || args->count > KVM_S390_SKEYS_MAX)
>>>                 return -EINVAL;
>>>
>>> -       keys = kmalloc_array(args->count, sizeof(uint8_t),
>>> -                            GFP_KERNEL | __GFP_NOWARN);
>>> -       if (!keys)
>>> -               keys = vmalloc(sizeof(uint8_t) * args->count);
>>> +       keys = kvmalloc(args->count * sizeof(uint8_t), GFP_KERNEL);
>>
>> Before doing this conversion, can we add a kvmalloc_array() API? This
>> conversion could allow for the reintroduction of integer overflow
>> flaws. (This particular situation isn't at risk since ->count is
>> checked, but I'd prefer we not create a risky set of examples for
>> using kvmalloc.)
> 
> Well, I am not opposed to kvmalloc_array but I would argue that this
> conversion cannot introduce new overflow issues. The code would have
> to be broken already because even though kmalloc_array checks for the
> overflow but vmalloc fallback doesn't...

Yeah I agree, but if some of the places were really wrong, after the
conversion we won't see them anymore.

> If there is a general interest for this API I can add it.

I think it would be better, yes.