linux-kernel - [PATCH] net: usb: asix: validate PHY address before use

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Message-ID: <20251217085057.270704-1-kartikey406@gmail.com>
Date: Wed, 17 Dec 2025 14:20:57 +0530
From: Deepanshu Kartikey <kartikey406@...il.com>
To: andrew+netdev@...n.ch,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	khalasa@...p.pl
Cc: o.rempel@...gutronix.de,
	linux-usb@...r.kernel.org,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Deepanshu Kartikey <kartikey406@...il.com>,
	syzbot+3d43c9066a5b54902232@...kaller.appspotmail.com
Subject: [PATCH] net: usb: asix: validate PHY address before use

The ASIX driver reads the PHY address from the USB device via
asix_read_phy_addr(). A malicious or faulty device can return an
invalid address (>= PHY_MAX_ADDR), which causes a warning in
mdiobus_get_phy():

  addr 207 out of range
  WARNING: drivers/net/phy/mdio_bus.c:76

Validate the PHY address before returning it from asix_read_phy_addr().

Reported-by: syzbot+3d43c9066a5b54902232@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3d43c9066a5b54902232
Tested-by: syzbot+3d43c9066a5b54902232@...kaller.appspotmail.com
Fixes: 7e88b11a862a ("net: usb: asix: refactor asix_read_phy_addr() and handle errors on return")
Signed-off-by: Deepanshu Kartikey <kartikey406@...il.com>
---
 drivers/net/usb/asix_common.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/usb/asix_common.c b/drivers/net/usb/asix_common.c
index 7fd763917ae2..6ab3486072cb 100644
--- a/drivers/net/usb/asix_common.c
+++ b/drivers/net/usb/asix_common.c
@@ -335,6 +335,11 @@ int asix_read_phy_addr(struct usbnet *dev, bool internal)
 	offset = (internal ? 1 : 0);
 	ret = buf[offset];
 
+	if (ret >= PHY_MAX_ADDR) {
+		netdev_err(dev->net, "invalid PHY address: %d\n", ret);
+		return -ENODEV;
+	}
+
 	netdev_dbg(dev->net, "%s PHY address 0x%x\n",
 		   internal ? "internal" : "external", ret);
 
-- 
2.43.0