net: asix: fix uninit value bugs

Syzbot reported uninit-value in asix_mdio_read(). The problem was in
missing error handling. asix_read_cmd() should initialize passed stack
variable smsr, but it can fail in some cases. Then while condidition
checks possibly uninit smsr variable.

Since smsr is uninitialized stack variable, driver can misbehave,
because smsr will be random in case of asix_read_cmd() failure.
Fix it by adding error handling and just continue the loop instead of
checking uninit value.

Added helper function for checking Host_En bit, since wrong loop was used
in 4 functions and there is no need in copy-pasting code parts.

Cc: Robert Foss <robert.foss@collabora.com>
Fixes: d9fe64e ("net: asix: Add in_pm parameter")
Reported-by: syzbot+a631ec9e717fb0423053@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/asix_common.c

@@ -63,6 +63,29 @@ void asix_write_cmd_async(struct usbnet *dev, u8 cmd, u16 value, u16 index,
 			       value, index, data, size);
 }
 
+static int asix_check_host_enable(struct usbnet *dev, int in_pm)
+{
+	int i, ret;
+	u8 smsr;
+
+	for (i = 0; i < 30; ++i) {
+		ret = asix_set_sw_mii(dev, in_pm);
+		if (ret == -ENODEV || ret == -ETIMEDOUT)
+			break;
+		usleep_range(1000, 1100);
+		ret = asix_read_cmd(dev, AX_CMD_STATMNGSTS_REG,
+				    0, 0, 1, &smsr, in_pm);
+		if (ret == -ENODEV)
+			break;
+		else if (ret < 0)
+			continue;
+		else if (smsr & AX_HOST_EN)
+			break;
+	}
+
+	return ret;
+}
+
 static void reset_asix_rx_fixup_info(struct asix_rx_fixup_info *rx)
 {
 	/* Reset the variables that have a lifetime outside of
@@ -467,19 +490,11 @@ int asix_mdio_read(struct net_device *netdev, int phy_id, int loc)
 {
 	struct usbnet *dev = netdev_priv(netdev);
 	__le16 res;
-	u8 smsr;
-	int i = 0;
 	int ret;
 
 	mutex_lock(&dev->phy_mutex);
-	do {
-		ret = asix_set_sw_mii(dev, 0);
-		if (ret == -ENODEV || ret == -ETIMEDOUT)
-			break;
-		usleep_range(1000, 1100);
-		ret = asix_read_cmd(dev, AX_CMD_STATMNGSTS_REG,
-				    0, 0, 1, &smsr, 0);
-	} while (!(smsr & AX_HOST_EN) && (i++ < 30) && (ret != -ENODEV));
+
+	ret = asix_check_host_enable(dev, 0);
 	if (ret == -ENODEV || ret == -ETIMEDOUT) {
 		mutex_unlock(&dev->phy_mutex);
 		return ret;
@@ -505,23 +520,14 @@ static int __asix_mdio_write(struct net_device *netdev, int phy_id, int loc,
 {
 	struct usbnet *dev = netdev_priv(netdev);
 	__le16 res = cpu_to_le16(val);
-	u8 smsr;
-	int i = 0;
 	int ret;
 
 	netdev_dbg(dev->net, "asix_mdio_write() phy_id=0x%02x, loc=0x%02x, val=0x%04x\n",
 			phy_id, loc, val);
 
 	mutex_lock(&dev->phy_mutex);
-	do {
-		ret = asix_set_sw_mii(dev, 0);
-		if (ret == -ENODEV)
-			break;
-		usleep_range(1000, 1100);
-		ret = asix_read_cmd(dev, AX_CMD_STATMNGSTS_REG,
-				    0, 0, 1, &smsr, 0);
-	} while (!(smsr & AX_HOST_EN) && (i++ < 30) && (ret != -ENODEV));
 
+	ret = asix_check_host_enable(dev, 0);
 	if (ret == -ENODEV)
 		goto out;
 
@@ -561,19 +567,11 @@ int asix_mdio_read_nopm(struct net_device *netdev, int phy_id, int loc)
 {
 	struct usbnet *dev = netdev_priv(netdev);
 	__le16 res;
-	u8 smsr;
-	int i = 0;
 	int ret;
 
 	mutex_lock(&dev->phy_mutex);
-	do {
-		ret = asix_set_sw_mii(dev, 1);
-		if (ret == -ENODEV || ret == -ETIMEDOUT)
-			break;
-		usleep_range(1000, 1100);
-		ret = asix_read_cmd(dev, AX_CMD_STATMNGSTS_REG,
-				    0, 0, 1, &smsr, 1);
-	} while (!(smsr & AX_HOST_EN) && (i++ < 30) && (ret != -ENODEV));
+
+	ret = asix_check_host_enable(dev, 1);
 	if (ret == -ENODEV || ret == -ETIMEDOUT) {
 		mutex_unlock(&dev->phy_mutex);
 		return ret;
@@ -595,22 +593,14 @@ asix_mdio_write_nopm(struct net_device *netdev, int phy_id, int loc, int val)
 {
 	struct usbnet *dev = netdev_priv(netdev);
 	__le16 res = cpu_to_le16(val);
-	u8 smsr;
-	int i = 0;
 	int ret;
 
 	netdev_dbg(dev->net, "asix_mdio_write() phy_id=0x%02x, loc=0x%02x, val=0x%04x\n",
 			phy_id, loc, val);
 
 	mutex_lock(&dev->phy_mutex);
-	do {
-		ret = asix_set_sw_mii(dev, 1);
-		if (ret == -ENODEV)
-			break;
-		usleep_range(1000, 1100);
-		ret = asix_read_cmd(dev, AX_CMD_STATMNGSTS_REG,
-				    0, 0, 1, &smsr, 1);
-	} while (!(smsr & AX_HOST_EN) && (i++ < 30) && (ret != -ENODEV));
+
+	ret = asix_check_host_enable(dev, 1);
 	if (ret == -ENODEV) {
 		mutex_unlock(&dev->phy_mutex);
 		return;