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

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>
Link: https://patch.msgid.link/20250818084541.1958-1-yuichtsu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/usb/asix_devices.c b/drivers/net/usb/asix_devices.c
index d9f5942..792ddda 100644 (file)
--- 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);