net: ch9200: fix uninitialised access during mii_nway_restart

In mii_nway_restart() the code attempts to call
mii->mdio_read which is ch9200_mdio_read(). ch9200_mdio_read()
utilises a local buffer called "buff", which is initialised
with control_read(). 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.

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>
Link: https://patch.msgid.link/20250526183607.66527-1-qasdev00@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/usb/ch9200.c b/drivers/net/usb/ch9200.c
index f69d9b902da04a88fdacb85baba32cec09a24fd9..a206ffa76f1b93a780b88b5fa619da68f1736209 100644 (file)
--- 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 < 0)
+               return ret;
 
        return (buff[0] | buff[1] << 8);
 }