Re: [PATCH][next] clk: imx: pll14xx: Fix potential integer overflow on multiplication

["Colin King (gmail)" <colin.i.king@gmail.com>]

On 07/10/2024 10:54, Dan Carpenter wrote:
> On Mon, Oct 07, 2024 at 09:48:40AM +0100, Colin Ian King wrote:
>> The calculation of fout is using int multiplication and assigning
>> the result to a u64, this can potentially overflow if the int variable
>> mdiv is too large. Fix this by making the 65536 a u64 value to ensure a
>> u64 multiplication is being performed to avoid the overflow.
>>
>> Fixes: 53990cf9d5b4 ("clk: imx: pll14xx: consolidate rate calculation")
>> Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
> 
> mdiv is always clamped in then 0-1023 range by one of these:
> 
> 	mdiv = FIELD_GET(MDIV_MASK, pll_div_ctl0);
> 	mdiv = clamp(mdiv, 64, 1023);
> 
> so it can't overflow and the Fixes tag is unnecessary.

Good point.

> 
> I think the reason why "fout" is declared as a u64 is because we were worried
> that on 32 bit systems the "fout *=" operation could overflow.  That looks
> reasonable to me.

Yes, that makes perfect sense. NAK my patch. Apologies for the noise.

Colin

> 
> regards,
> dan carpenter
>