Re: [PATCH][next] dmaengine: ti: k3-udma: Use struct_size() in kzalloc()

[Peter Ujfalusi <peter.ujfalusi@ti.com>]

On 26/06/2020 16.29, Gustavo A. R. Silva wrote:
> Hi Peter,
> 
> Please, see my comments below...
> 
> On Fri, Jun 26, 2020 at 10:30:37AM +0300, Peter Ujfalusi wrote:
>>
>>
>> On 24/06/2020 20.12, Gustavo A. R. Silva wrote:
>>> Hi Vinod,
>>>
>>> On 6/24/20 00:55, Vinod Koul wrote:
>>>> On 19-06-20, 17:43, Gustavo A. R. Silva wrote:
>>>>> Make use of the struct_size() helper instead of an open-coded version
>>>>> in order to avoid any potential type mistakes.
>>>>>
>>>>> This code was detected with the help of Coccinelle and, audited and
>>>>> fixed manually.
>>>>>
>>>>> Addresses-KSPP-ID: https://github.com/KSPP/linux/issues/83
>>>>> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
>>>>> ---
>>>>>  drivers/dma/ti/k3-udma.c | 4 ++--
>>>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/dma/ti/k3-udma.c b/drivers/dma/ti/k3-udma.c
>>>>> index 0d5fb154b8e2..411c54b86ba8 100644
>>>>> --- a/drivers/dma/ti/k3-udma.c
>>>>> +++ b/drivers/dma/ti/k3-udma.c
>>>>> @@ -2209,7 +2209,7 @@ udma_prep_slave_sg_pkt(struct udma_chan *uc, struct scatterlist *sgl,
>>>>>  	u32 ring_id;
>>>>>  	unsigned int i;
>>>>>  
>>>>> -	d = kzalloc(sizeof(*d) + sglen * sizeof(d->hwdesc[0]), GFP_NOWAIT);
>>>>> +	d = kzalloc(struct_size(d, hwdesc, sglen), GFP_NOWAIT);
>>>>
>>>> struct_size() is a * b + c but here we need, a + b * c.. the trailing
>>>> struct is N times here..
>>>>
>>>
>>> struct_size() works exactly as expected in this case. :)
>>> Please, see:
>>>
>>> include/linux/overflow.h:314:
>>> 314 #define struct_size(p, member, count)                                   \
>>> 315         __ab_c_size(count,                                              \
>>> 316                     sizeof(*(p)->member) + __must_be_array((p)->member),\
>>> 317                     sizeof(*(p)))
>>
>> True, struct_size is for this sort of things.
>>
>> Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
>>
>> While looking it up in include/linux/overflow.h I have noticed your
>> commit in linux-next, which adds flex_array_size()
>>
>> The example in the commit message contradicts with what the helper
> 
> There is no contradiction here.
> 
>> does imho. To be correct it should have been:
>>
>> struct something {
>> 	size_t count;
>> 	struct foo items[];
>> };
>>
>> - struct something *instance;
>> + struct something instance;
>>
>> - instance = kmalloc(struct_size(instance, items, count), GFP_KERNEL);
>> + instance.items = kmalloc(struct_size(instance, items, count), GFP_KERNEL);
>> instance->count = count;
>> memcpy(instance->items, src, flex_array_size(instance, items, instance->count));
>>
> 
> This is all wrong. Please, double check how struct_size() works.

Yes, I got it mixed up, I know how struct_size works... For some reason
I just overlooked it's use in the kmalloc().

> 
> Thanks
> --
> Gustavo
> 
>>>>>  	if (!d)
>>>>>  		return NULL;
>>>>>  
>>>>> @@ -2525,7 +2525,7 @@ udma_prep_dma_cyclic_pkt(struct udma_chan *uc, dma_addr_t buf_addr,
>>>>>  	if (period_len >= SZ_4M)
>>>>>  		return NULL;
>>>>>  
>>>>> -	d = kzalloc(sizeof(*d) + periods * sizeof(d->hwdesc[0]), GFP_NOWAIT);
>>>>> +	d = kzalloc(struct_size(d, hwdesc, periods), GFP_NOWAIT);
>>>>>  	if (!d)
>>>>>  		return NULL;
>>>>>  
>>>>> -- 
>>>>> 2.27.0
>>>>
>>
>> - Péter
>>
>> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
>>

- Péter

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki