[PATCH] net: usb: asix_devices: Fix PHY address mask in MDIO bus initialization

[PATCH] net: usb: asix_devices: Fix PHY address mask in MDIO bus initialization

[Yuichiro Tsuji]

Syzbot reported shift-out-of-bounds exception on MDIO bus initialization.

The PHY address should be masked to 5 bits (0-31). Without this
mask, invalid PHY addresses could be used, potentially causing issues
with MDIO bus operations.

Fix this by masking the PHY address with 0x1f (31 decimal) to ensure
it stays within the valid range.

Fixes: 4faff70959d5 ("net: usb: asix_devices: add phy_mask for ax88772 mdio bus")
Reported-by: syzbot+20537064367a0f98d597@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=20537064367a0f98d597
Tested-by: syzbot+20537064367a0f98d597@syzkaller.appspotmail.com
Signed-off-by: Yuichiro Tsuji <yuichtsu@amazon.com>
---
 drivers/net/usb/asix_devices.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/usb/asix_devices.c b/drivers/net/usb/asix_devices.c
index d9f5942ccc44..792ddda1ad49 100644
--- a/drivers/net/usb/asix_devices.c
+++ b/drivers/net/usb/asix_devices.c
@@ -676,7 +676,7 @@ static int ax88772_init_mdio(struct usbnet *dev)
 	priv->mdio->read = &asix_mdio_bus_read;
 	priv->mdio->write = &asix_mdio_bus_write;
 	priv->mdio->name = "Asix MDIO Bus";
-	priv->mdio->phy_mask = ~(BIT(priv->phy_addr) | BIT(AX_EMBD_PHY_ADDR));
+	priv->mdio->phy_mask = ~(BIT(priv->phy_addr & 0x1f) | BIT(AX_EMBD_PHY_ADDR));
 	/* mii bus name is usb-<usb bus number>-<usb device number> */
 	snprintf(priv->mdio->id, MII_BUS_ID_SIZE, "usb-%03d:%03d",
 		 dev->udev->bus->busnum, dev->udev->devnum);
-- 
2.43.5

Re: [PATCH] net: usb: asix_devices: Fix PHY address mask in MDIO bus initialization

[Andrew Lunn]

On Mon, Aug 18, 2025 at 05:45:07PM +0900, Yuichiro Tsuji wrote:
> Syzbot reported shift-out-of-bounds exception on MDIO bus initialization.
> 
> The PHY address should be masked to 5 bits (0-31). Without this
> mask, invalid PHY addresses could be used, potentially causing issues
> with MDIO bus operations.
> 
> Fix this by masking the PHY address with 0x1f (31 decimal) to ensure
> it stays within the valid range.
> 
> Fixes: 4faff70959d5 ("net: usb: asix_devices: add phy_mask for ax88772 mdio bus")
> Reported-by: syzbot+20537064367a0f98d597@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=20537064367a0f98d597
> Tested-by: syzbot+20537064367a0f98d597@syzkaller.appspotmail.com
> Signed-off-by: Yuichiro Tsuji <yuichtsu@amazon.com>

Reviewed-by: Andrew Lunn <andrew@lunn.ch>

    Andrew

Re: [PATCH] net: usb: asix_devices: Fix PHY address mask in MDIO bus initialization

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Mon, 18 Aug 2025 17:45:07 +0900 you wrote:
> Syzbot reported shift-out-of-bounds exception on MDIO bus initialization.
> 
> The PHY address should be masked to 5 bits (0-31). Without this
> mask, invalid PHY addresses could be used, potentially causing issues
> with MDIO bus operations.
> 
> Fix this by masking the PHY address with 0x1f (31 decimal) to ensure
> it stays within the valid range.
> 
> [...]

Here is the summary with links:
  - net: usb: asix_devices: Fix PHY address mask in MDIO bus initialization
    https://git.kernel.org/netdev/net/c/24ef2f53c07f

You are awesome, thank you!
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