[PATCH] net: fix uninitialised access in mii_nway_restart() and cleanup error handling

[Qasim Ijaz <qasdev00@gmail.com>]

In mii_nway_restart() during the line:

        bmcr = mii->mdio_read(mii->dev, mii->phy_id, MII_BMCR);

The code attempts to call mii->mdio_read which is ch9200_mdio_read().

ch9200_mdio_read() utilises a local buffer, which is initialised
with control_read():

        unsigned char buff[2];

However buff is conditionally initialised inside control_read():

        if (err == size) {
                memcpy(data, buf, size);
        }

If the condition of "err == size" is not met, then buff remains
uninitialised. Once this happens the uninitialised buff is accessed
and returned during ch9200_mdio_read():

        return (buff[0] | buff[1] << 8);

The problem stems from the fact that ch9200_mdio_read() ignores the
return value of control_read(), leading to uinit-access of buff.

To fix this we should check the return value of control_read()
and return early on error.

Furthermore the get_mac_address() function has a similar problem where
it does not directly check the return value of each control_read(),
instead it sums up the return values and checks them all at the end
which means if any call to control_read() fails the function just 
continues on.

Handle this by validating the return value of each call and fail fast
and early instead of continuing.

Lastly ch9200_bind() ignores the return values of multiple 
control_write() calls.

Validate each control_write() call to ensure it succeeds before
continuing with the next call.

Reported-by: syzbot <syzbot+3361c2d6f78a3e0892f9@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=3361c2d6f78a3e0892f9
Tested-by: syzbot <syzbot+3361c2d6f78a3e0892f9@syzkaller.appspotmail.com>
Fixes: 4a476bd6d1d9 ("usbnet: New driver for QinHeng CH9200 devices")
Cc: stable@vger.kernel.org
Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
---
 drivers/net/mii.c        |  2 ++
 drivers/net/usb/ch9200.c | 55 +++++++++++++++++++++++++++-------------
 2 files changed, 40 insertions(+), 17 deletions(-)

diff --git a/drivers/net/mii.c b/drivers/net/mii.c
index 37bc3131d31a..e305bf0f1d04 100644
--- a/drivers/net/mii.c
+++ b/drivers/net/mii.c
@@ -464,6 +464,8 @@ int mii_nway_restart (struct mii_if_info *mii)
 
 	/* if autoneg is off, it's an error */
 	bmcr = mii->mdio_read(mii->dev, mii->phy_id, MII_BMCR);
+	if (bmcr < 0)
+		return bmcr;
 
 	if (bmcr & BMCR_ANENABLE) {
 		bmcr |= BMCR_ANRESTART;
diff --git a/drivers/net/usb/ch9200.c b/drivers/net/usb/ch9200.c
index f69d9b902da0..e938501a1fc8 100644
--- a/drivers/net/usb/ch9200.c
+++ b/drivers/net/usb/ch9200.c
@@ -178,6 +178,7 @@ static int ch9200_mdio_read(struct net_device *netdev, int phy_id, int loc)
 {
 	struct usbnet *dev = netdev_priv(netdev);
 	unsigned char buff[2];
+	int ret;
 
 	netdev_dbg(netdev, "%s phy_id:%02x loc:%02x\n",
 		   __func__, phy_id, loc);
@@ -185,8 +186,10 @@ static int ch9200_mdio_read(struct net_device *netdev, int phy_id, int loc)
 	if (phy_id != 0)
 		return -ENODEV;
 
-	control_read(dev, REQUEST_READ, 0, loc * 2, buff, 0x02,
-		     CONTROL_TIMEOUT_MS);
+	ret = control_read(dev, REQUEST_READ, 0, loc * 2, buff, 0x02,
+			   CONTROL_TIMEOUT_MS);
+	if (ret != 2)
+		return ret;
 
 	return (buff[0] | buff[1] << 8);
 }
@@ -303,24 +306,27 @@ static int ch9200_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 
 static int get_mac_address(struct usbnet *dev, unsigned char *data)
 {
-	int err = 0;
 	unsigned char mac_addr[0x06];
-	int rd_mac_len = 0;
+	int rd_mac_len;
 
 	netdev_dbg(dev->net, "%s:\n\tusbnet VID:%0x PID:%0x\n", __func__,
 		   le16_to_cpu(dev->udev->descriptor.idVendor),
 		   le16_to_cpu(dev->udev->descriptor.idProduct));
 
-	memset(mac_addr, 0, sizeof(mac_addr));
-	rd_mac_len = control_read(dev, REQUEST_READ, 0,
-				  MAC_REG_STATION_L, mac_addr, 0x02,
-				  CONTROL_TIMEOUT_MS);
-	rd_mac_len += control_read(dev, REQUEST_READ, 0, MAC_REG_STATION_M,
-				   mac_addr + 2, 0x02, CONTROL_TIMEOUT_MS);
-	rd_mac_len += control_read(dev, REQUEST_READ, 0, MAC_REG_STATION_H,
-				   mac_addr + 4, 0x02, CONTROL_TIMEOUT_MS);
-	if (rd_mac_len != ETH_ALEN)
-		err = -EINVAL;
+	rd_mac_len = control_read(dev, REQUEST_READ, 0, MAC_REG_STATION_L,
+				  mac_addr, 0x02, CONTROL_TIMEOUT_MS);
+	if (rd_mac_len != 2)
+		return rd_mac_len;
+
+	rd_mac_len = control_read(dev, REQUEST_READ, 0, MAC_REG_STATION_M,
+				  mac_addr + 2, 0x02, CONTROL_TIMEOUT_MS);
+	if (rd_mac_len != 2)
+		return rd_mac_len;
+
+	rd_mac_len = control_read(dev, REQUEST_READ, 0, MAC_REG_STATION_H,
+				  mac_addr + 4, 0x02, CONTROL_TIMEOUT_MS);
+	if (rd_mac_len != 2)
+		return rd_mac_len;
 
 	data[0] = mac_addr[5];
 	data[1] = mac_addr[4];
@@ -329,12 +335,12 @@ static int get_mac_address(struct usbnet *dev, unsigned char *data)
 	data[4] = mac_addr[1];
 	data[5] = mac_addr[0];
 
-	return err;
+	return 0;
 }
 
 static int ch9200_bind(struct usbnet *dev, struct usb_interface *intf)
 {
-	int retval = 0;
+	int retval;
 	unsigned char data[2];
 	u8 addr[ETH_ALEN];
 
@@ -357,37 +363,52 @@ static int ch9200_bind(struct usbnet *dev, struct usb_interface *intf)
 	data[1] = 0x0F;
 	retval = control_write(dev, REQUEST_WRITE, 0, MAC_REG_THRESHOLD, data,
 			       0x02, CONTROL_TIMEOUT_MS);
+	if (retval)
+		return retval;
 
 	data[0] = 0xA0;
 	data[1] = 0x90;
 	retval = control_write(dev, REQUEST_WRITE, 0, MAC_REG_FIFO_DEPTH, data,
 			       0x02, CONTROL_TIMEOUT_MS);
+	if (retval)
+		return retval;
 
 	data[0] = 0x30;
 	data[1] = 0x00;
 	retval = control_write(dev, REQUEST_WRITE, 0, MAC_REG_PAUSE, data,
 			       0x02, CONTROL_TIMEOUT_MS);
+	if (retval)
+		return retval;
 
 	data[0] = 0x17;
 	data[1] = 0xD8;
 	retval = control_write(dev, REQUEST_WRITE, 0, MAC_REG_FLOW_CONTROL,
 			       data, 0x02, CONTROL_TIMEOUT_MS);
+	if (retval)
+		return retval;
 
 	/* Undocumented register */
 	data[0] = 0x01;
 	data[1] = 0x00;
 	retval = control_write(dev, REQUEST_WRITE, 0, 254, data, 0x02,
 			       CONTROL_TIMEOUT_MS);
+	if (retval)
+		return retval;
 
 	data[0] = 0x5F;
 	data[1] = 0x0D;
 	retval = control_write(dev, REQUEST_WRITE, 0, MAC_REG_CTRL, data, 0x02,
 			       CONTROL_TIMEOUT_MS);
+	if (retval)
+		return retval;
 
 	retval = get_mac_address(dev, addr);
+	if (retval)
+		return retval;
+
 	eth_hw_addr_set(dev->net, addr);
 
-	return retval;
+	return 0;
 }
 
 static const struct driver_info ch9200_info = {
-- 
2.39.5