Skip to contentSkip to conversation

net: fix uninitialised access in mii_nway_restart()

PATCH New Qasim Ijaz 1 participant 1 message Mar 19, 2025 1 message not in the archive

Subsystems (3)
Network drivers Stable branch USB networking drivers
lore
Share & tools
lore

A message that is not in the archive (sent off-list or not yet received): [email protected]

Qasim Ijaz

author
#1 lore raw

PATCH 1/4 net: fix uninitialised access in mii_nway_restart()

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.

Reported-by syzbot <[email protected]>
Closes https://syzkaller.appspot.com/bug?extid=3361c2d6f78a3e0892f9
Tested-by syzbot <[email protected]>
Fixes 4a476bd6d1d9 ("usbnet: New driver for QinHeng CH9200 devices")
Cc [email protected]
Signed-off-by Qasim Ijaz <[email protected]>
---
 drivers/net/mii.c        | 2 ++
 drivers/net/usb/ch9200.c | 7 +++++--
 2 files changed, 7 insertions(+), 2 deletions(-)
drivers/net/mii.c +2 -0
index 37bc3131d31a..e305bf0f1d04 100644
@@ -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;
drivers/net/usb/ch9200.c +5 -2
index f69d9b902da0..a206ffa76f1b 100644
@@ -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);
 }
Signature · 1 line
2.39.5