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

[Colin King (gmail)]

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@xxxxxxxxx>
>
> 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