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SubjectRe: [PATCH v11 5/8] iio: adc: adi-axi-adc: add support for AXI ADC IP core
On Sun, Mar 22, 2020 at 12:45:39PM +0200, Andy Shevchenko wrote:
> +Cc Kees (see below about allocation size checks)
>
> On Sun, Mar 22, 2020 at 11:36 AM Ardelean, Alexandru
> <alexandru.Ardelean@analog.com> wrote:
> > On Sat, 2020-03-21 at 23:38 +0200, Andy Shevchenko wrote:
> > > On Sat, Mar 21, 2020 at 10:55 AM Alexandru Ardelean
> > > <alexandru.ardelean@analog.com> wrote:
>
> ...
>
> > > > +static struct adi_axi_adc_conv *adi_axi_adc_conv_register(struct device
> > > > *dev,
> > > > + int sizeof_priv)
> > > > +{
> > > > + struct adi_axi_adc_client *cl;
> > > > + size_t alloc_size;
> > > > +
> > > > + alloc_size = sizeof(struct adi_axi_adc_client);
> > > > + if (sizeof_priv) {
> > > > + alloc_size = ALIGN(alloc_size, IIO_ALIGN);
> > > > + alloc_size += sizeof_priv;
> > > > + }
> > > > + alloc_size += IIO_ALIGN - 1;
> > >
> > > Have you looked at linux/overflow.h?
> >
> > i did now;
> > any hints where i should look closer?
>
> It seems it lacks of this kind of allocation size checks... Perhaps add one?
> Kees, what do you think?
>
> > > > + cl = kzalloc(alloc_size, GFP_KERNEL);
> > > > + if (!cl)
> > > > + return ERR_PTR(-ENOMEM);

My head hurts trying to read this! ;) Okay, so the base size is
sizeof(struct adi_axi_adc_client). But if sizeof_priv is non-zero
(this arg should be size_t not int), then we need to make the struct
size ALIGNed? And then what is the "+= IIO_ALIGN - 1" for?

It's not clear to me what the expect alignment/padding is here.

I would probably construct this as:

sizeof_self = sizeof(struct adi_axi_adc_client);
if (sizeof_priv)
sizeof_self = ALIGN(sizeof_self, IIO_ALIGN);
if (check_add_overflow(sizeof_self, sizeof_priv, &sizeof_alloc))
return ERR_PTR(-ENOMEM);
if (check_add_overflow(sizeof_alloc, IIO_ALIGN - 1, &sizeof_alloc))
return ERR_PTR(-ENOMEM);

But I don't understand the "IIO_ALIGN - 1" part, so I assume this could
be shortened with better use of ALIGN()?

Also, this feels like a weird driver allocation overall:

+ struct adi_axi_adc_conv **ptr, *conv;
+
+ ptr = devres_alloc(devm_adi_axi_adc_conv_release, sizeof(*ptr),
+ GFP_KERNEL);
+ if (!ptr)
+ return ERR_PTR(-ENOMEM);
+
+ conv = adi_axi_adc_conv_register(dev, sizeof_priv);

devres_alloc() allocates storage for a _single pointer_. :P That's not
useful for resource tracking. Why is devres_alloc() being called here
and not down in adi_axi_adc_conv_register() and just passing the pointer
back up?

--
Kees Cook

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