netdev - Re: [PATCH net-next] net: phy: mdio-bcm-unimac: Cast denominator to unsigned long to avoid overflow

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Message-ID: <df295be9-d33e-45d2-914f-c9c1554e5ac0@gmail.com>
Date: Tue, 12 Mar 2024 10:23:06 -0700
From: Florian Fainelli <f.fainelli@...il.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>,
 Daniil Dulov <d.dulov@...ddin.ru>
Cc: Jakub Kicinski <kuba@...nel.org>,
 Florian Fainelli <florian.fainelli@...adcom.com>,
 Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>, Andrew Lunn <andrew@...n.ch>,
 Heiner Kallweit <hkallweit1@...il.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Doug Berger <opendmb@...il.com>, Paolo Abeni <pabeni@...hat.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 lvc-project@...uxtesting.org
Subject: Re: [PATCH net-next] net: phy: mdio-bcm-unimac: Cast denominator to
 unsigned long to avoid overflow

On 3/12/24 10:18, Russell King (Oracle) wrote:
> On Tue, Mar 12, 2024 at 07:53:58PM +0300, Daniil Dulov wrote:
>> The expression priv->clk_freq * 2 can lead to overflow that will cause
>> a division by zero. So, let's cast it to unsigned long to avoid it.
> 
> How does casting this help? "unsigned long" can still be 32-bit.
> Maybe unimac_mdio_probe() should be validating the value it read from
> DT won't overflow? I suspect that a value of 2.1GHz is way too large
> for this property in any case.
> 
> https://en.wikipedia.org/wiki/Management_Data_Input/Output#Electrical_specification
> 
> (note, this driver is clause-22 only.)
> 

Had commented on the previous version (not sure why this was not 
prefixed with v2) that the maximum clock frequency for this clock is 
250MHz, the driver could check that to prevent for an overflow, most 
certainly.
-- 
Florian