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

[Michal Hocko]

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...

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

-- 
Michal Hocko
SUSE Labs