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

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Message-ID: <aDVt5LZe-jo7mVxt@stanley.mountain>
Date: Tue, 27 May 2025 10:46:44 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Subbaraya Sundeep <sbhatta@...vell.com>
Cc: Eugenia Emantayev <eugenia@...lanox.com>,
	Tariq Toukan <tariqt@...dia.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Matan Barak <matanb@...lanox.com>, netdev@...r.kernel.org,
	linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH net] net/mlx4_en: Prevent potential integer overflow
 calculating Hz

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@...aro.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@...aro.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