Re: [PATCH v4 06/21] hwmon: (mr75203) fix multi-channel voltage reading
From: Andy Shevchenko
Date: Wed Sep 07 2022 - 10:42:37 EST
On Wed, Sep 07, 2022 at 08:15:36AM +0300, Farber, Eliav wrote:
> On 9/6/2022 5:10 PM, Andy Shevchenko wrote:
> > On Tue, Sep 06, 2022 at 08:33:41AM +0000, Eliav Farber wrote:
...
> > > + total_ch = ch_num * vm_num;
> > > + in_config = devm_kcalloc(dev, total_ch + 1,
> > > sizeof(*in_config), GFP_KERNEL);
> >
> > Strictly speaking this should be `size_add(size_mul(...) ...)`
> > construction
> > from overflow.h.
> >
> > total_ch = size_mul(ch_num, vm_num);
> > in_config = devm_kcalloc(dev, size_add(total_ch, 1),
> > sizeof(*in_config), GFP_KERNEL);
> >
> > Alternatively before doing all these, add a check
> >
> > if (array3_size(ch_num, vm_num, sizeof(*in_config)) <
> > SIZE_MAX - sizeof(*in_config))
> > return -EOVERFLOW;
> >
> > But this is a bit monstrous. Seems like the above looks and feels better.
> >
> > Also for backporting purposes perhaps it's fine to do without using
> > those macro
> > helpers.
> According to the driver code total_ch is a u32 variable while vm_num
> and ch_num are both limited to a value of 31:
>
> #define VM_NUM_MSK GENMASK(20, 16)
> #define VM_NUM_SFT 16
> #define CH_NUM_MSK GENMASK(31, 24)
> #define CH_NUM_SFT 24
>
> In addition the PVT Controller Series 3+ Specification mentions that
> the actual maximum values are even smaller – 8 for vm_num and 16 for
> ch_num.
> Therefore we are very far from a scenario of an overflow.
> Do you still think overflow protection in necessary?
Like I said "Strictly..." Means it's up to you, but allocations are
usually be protected against the overflows.
--
With Best Regards,
Andy Shevchenko