Re: [PATCH net] net/mlx4_en: Prevent potential integer overflow calculating Hz

[Dan Carpenter <dan.carpenter@linaro.org>]

On Tue, May 27, 2025 at 07:31:22AM +0000, Subbaraya Sundeep wrote:
> Hi,
> 
> On 2025-05-27 at 05:51:38, Dan Carpenter (dan.carpenter@linaro.org) wrote:
> > The "freq" variable is in terms of MHz and "max_val_cycles" is in terms
> > of Hz.  The fact that "max_val_cycles" is a u64 suggests that support
> > for high frequency is intended but the "freq_khz * 1000" would overflow
> > the u32 type if we went above 4GHz.  Use unsigned long type for the
> > mutliplication to prevent that.
> > 
> > Fixes: 31c128b66e5b ("net/mlx4_en: Choose time-stamping shift value according to HW frequency")
> > Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
> > ---
> >  drivers/net/ethernet/mellanox/mlx4/en_clock.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/ethernet/mellanox/mlx4/en_clock.c b/drivers/net/ethernet/mellanox/mlx4/en_clock.c
> > index cd754cd76bde..7abd6a7c9ebe 100644
> > --- a/drivers/net/ethernet/mellanox/mlx4/en_clock.c
> > +++ b/drivers/net/ethernet/mellanox/mlx4/en_clock.c
> > @@ -249,7 +249,7 @@ static const struct ptp_clock_info mlx4_en_ptp_clock_info = {
> >  static u32 freq_to_shift(u16 freq)
> >  {
> >  	u32 freq_khz = freq * 1000;
> > -	u64 max_val_cycles = freq_khz * 1000 * MLX4_EN_WRAP_AROUND_SEC;
> > +	u64 max_val_cycles = freq_khz * 1000UL * MLX4_EN_WRAP_AROUND_SEC;
> 
> 1000ULL would be better then.

Yeah, that's true.

regards,
dan carpenter