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

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

[Daniil Dulov]

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.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: b78ac6ecd1b6 ("net: phy: mdio-bcm-unimac: Allow configuring MDIO clock divider")
Signed-off-by: Daniil Dulov <d.dulov@aladdin.ru>
---
 drivers/net/mdio/mdio-bcm-unimac.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/mdio/mdio-bcm-unimac.c b/drivers/net/mdio/mdio-bcm-unimac.c
index 68f8ee0ec8ba..055102e6bb6d 100644
--- a/drivers/net/mdio/mdio-bcm-unimac.c
+++ b/drivers/net/mdio/mdio-bcm-unimac.c
@@ -192,7 +192,7 @@ static void unimac_mdio_clk_set(struct unimac_mdio_priv *priv)
 	else
 		rate = clk_get_rate(priv->clk);
 
-	div = (rate / (2 * priv->clk_freq)) - 1;
+	div = (rate / (2 * (unsigned long)priv->clk_freq)) - 1;
 	if (div & ~MDIO_CLK_DIV_MASK) {
 		pr_warn("Incorrect MDIO clock frequency, ignoring\n");
 		return;
-- 
2.25.1

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

[Florian Fainelli]

[-- Attachment #1: Type: text/plain, Size: 575 bytes --]



On 3/7/2024 5:19 AM, 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.

It will not in real life because the maximum clock frequency is 250MHz, 
but it also does not hurt.

> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: b78ac6ecd1b6 ("net: phy: mdio-bcm-unimac: Allow configuring MDIO clock divider")
> Signed-off-by: Daniil Dulov <d.dulov@aladdin.ru>

Acked-by: Florian Fainelli <florian.fainelli@broadcom.com>
-- 
Florian

[-- Attachment #2: S/MIME Cryptographic Signature --]
[-- Type: application/pkcs7-signature, Size: 4221 bytes --]

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

[Jakub Kicinski]

On Thu, 7 Mar 2024 12:21:26 -0800 Florian Fainelli wrote:
> On 3/7/2024 5:19 AM, 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.  
> 
> It will not in real life because the maximum clock frequency is 250MHz, 
> but it also does not hurt.

If that's the case - Daniil, could you respin against net-next without
the Fixes tag? Otherwise it'll cause a conflict, if it's not a real
issue no point creating an extra hassle.
-- 
pw-bot: cr