[PATCH net-next v1 1/1] net: usb: lan78xx: fix possible NULL pointer dereference in lan78xx_phy_init()

[PATCH net-next v1 1/1] net: usb: lan78xx: fix possible NULL pointer dereference in lan78xx_phy_init()

[Oleksij Rempel]

If no PHY device is found (e.g., for LAN7801 in fixed-link mode),
lan78xx_phy_init() may proceed to dereference a NULL phydev pointer,
leading to a crash.

Update the logic to perform MAC configuration first, then check for the presence
of a PHY. For the fixed-link case, set up the fixed link and return early,
bypassing any code that assumes a valid phydev pointer.

It is safe to move lan78xx_mac_prepare_for_phy() earlier because this function
only uses information from dev->interface, which is configured by
lan78xx_get_phy() beforehand. The function does not access phydev or any data
set up by later steps.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 drivers/net/usb/lan78xx.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index ae37cd235526..6e9dc30b50f9 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -2831,6 +2831,10 @@ static int lan78xx_phy_init(struct lan78xx_net *dev)
 	if (ret < 0)
 		return ret;
 
+	ret = lan78xx_mac_prepare_for_phy(dev);
+	if (ret < 0)
+		goto phylink_uninit;
+
 	/* If no PHY is found, set up a fixed link. It is very specific to
 	 * the LAN7801 and is used in special cases like EVB-KSZ9897-1 where
 	 * LAN7801 acts as a USB-to-Ethernet interface to a switch without
@@ -2840,11 +2844,12 @@ static int lan78xx_phy_init(struct lan78xx_net *dev)
 		ret = lan78xx_set_fixed_link(dev);
 		if (ret < 0)
 			goto phylink_uninit;
-	}
 
-	ret = lan78xx_mac_prepare_for_phy(dev);
-	if (ret < 0)
-		goto phylink_uninit;
+		/* No PHY found, so set up a fixed link and return early.
+		 * No need to configure PHY IRQ or attach to phylink.
+		 */
+		return 0;
+	}
 
 	/* if phyirq is not set, use polling mode in phylib */
 	if (dev->domain_data.phyirq > 0)
-- 
2.39.5

Re: [PATCH net-next v1 1/1] net: usb: lan78xx: fix possible NULL pointer dereference in lan78xx_phy_init()

[Paolo Abeni]

On 6/26/25 12:37 PM, Oleksij Rempel wrote:
> If no PHY device is found (e.g., for LAN7801 in fixed-link mode),
> lan78xx_phy_init() may proceed to dereference a NULL phydev pointer,
> leading to a crash.
> 
> Update the logic to perform MAC configuration first, then check for the presence
> of a PHY. For the fixed-link case, set up the fixed link and return early,
> bypassing any code that assumes a valid phydev pointer.
> 
> It is safe to move lan78xx_mac_prepare_for_phy() earlier because this function
> only uses information from dev->interface, which is configured by
> lan78xx_get_phy() beforehand. The function does not access phydev or any data
> set up by later steps.
> 
> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>

Looks good, but this IMHO deserves a Fixes tag - yep, even for net-next!

Could you please share it?

Thanks,

Paolo

Re: [PATCH net-next v1 1/1] net: usb: lan78xx: fix possible NULL pointer dereference in lan78xx_phy_init()

[Oleksij Rempel]

On Tue, Jul 01, 2025 at 11:15:29AM +0200, Paolo Abeni wrote:
> On 6/26/25 12:37 PM, Oleksij Rempel wrote:
> > If no PHY device is found (e.g., for LAN7801 in fixed-link mode),
> > lan78xx_phy_init() may proceed to dereference a NULL phydev pointer,
> > leading to a crash.
> > 
> > Update the logic to perform MAC configuration first, then check for the presence
> > of a PHY. For the fixed-link case, set up the fixed link and return early,
> > bypassing any code that assumes a valid phydev pointer.
> > 
> > It is safe to move lan78xx_mac_prepare_for_phy() earlier because this function
> > only uses information from dev->interface, which is configured by
> > lan78xx_get_phy() beforehand. The function does not access phydev or any data
> > set up by later steps.
> > 
> > Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> > Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
> 
> Looks good, but this IMHO deserves a Fixes tag - yep, even for net-next!
> 
> Could you please share it?

Fixes: e110bc825897 ("net: usb: lan78xx: Convert to PHYLINK for improved PHY and MAC management")

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Re: [PATCH net-next v1 1/1] net: usb: lan78xx: fix possible NULL pointer dereference in lan78xx_phy_init()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Thu, 26 Jun 2025 12:37:31 +0200 you wrote:
> If no PHY device is found (e.g., for LAN7801 in fixed-link mode),
> lan78xx_phy_init() may proceed to dereference a NULL phydev pointer,
> leading to a crash.
> 
> Update the logic to perform MAC configuration first, then check for the presence
> of a PHY. For the fixed-link case, set up the fixed link and return early,
> bypassing any code that assumes a valid phydev pointer.
> 
> [...]

Here is the summary with links:
  - [net-next,v1,1/1] net: usb: lan78xx: fix possible NULL pointer dereference in lan78xx_phy_init()
    https://git.kernel.org/netdev/net-next/c/c22f056e49d9

You are awesome, thank you!
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