Subject: [PATCH v3] net: asix: fix uninit value bugs

From: Pavel Skripkin <[email-masked]>
Date: Sat, 14 Aug 2021 16:55:05 +0300

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.

Also, same loop was used in 3 other functions. Fixed uninit value bug
in them too.

Cc: Robert Foss <[email-masked]>
Fixes: d9fe64e51114 ("net: asix: Add in_pm parameter")
Reported-by: [email-masked]
Signed-off-by: Pavel Skripkin <[email-masked]>
---

Changes in v2:
	1. Fixed previous wrong approach and changed while loop to for loop
	2. Reported-and-tested-by: tag removed, since KMSAN tests can be
	   false positive. Used Reported-by instead.

Changes in v3:
	1. Addressed uninit value bugs in asix_mdio_write(), asix_mdio_read_nopm()
	and asix_mdio_write_nopm()
	2. Moved i after ret to reverse xmas tree style
	3. Fixed Fixes: tag

---
 drivers/net/usb/asix_common.c | 51 ++++++++++++++++++++++++++---------
 1 file changed, 39 insertions(+), 12 deletions(-)

diff --git a/drivers/net/usb/asix_common.c b/drivers/net/usb/asix_common.c
index ac92bc52a85e..f0ee35edb746 100644
--- a/drivers/net/usb/asix_common.c
+++ b/drivers/net/usb/asix_common.c
@@ -468,18 +468,25 @@ 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;
+	int i;
 
 	mutex_lock(&dev->phy_mutex);
-	do {
+	for (i = 0; i < 30; ++i) {
 		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));
+		if (ret == -ENODEV)
+			break;
+		else if (ret < 0)
+			continue;
+		else if (smsr & AX_HOST_EN)
+			break;
+	}
+
 	if (ret == -ENODEV || ret == -ETIMEDOUT) {
 		mutex_unlock(&dev->phy_mutex);
 		return ret;
@@ -506,21 +513,27 @@ 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;
+	int i;
 
 	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 {
+	for (i = 0; i < 30; ++i) {
 		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));
+		if (ret == -ENODEV)
+			break;
+		else if (ret < 0)
+			continue;
+		else if (smsr & AX_HOST_EN)
+			break;
+	}
 
 	if (ret == -ENODEV)
 		goto out;
@@ -562,18 +575,25 @@ 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;
+	int i;
 
 	mutex_lock(&dev->phy_mutex);
-	do {
+	for (i = 0; i < 30; ++i) {
 		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));
+		if (ret == -ENODEV)
+			break;
+		else if (ret < 0)
+			continue;
+		else if (smsr & AX_HOST_EN)
+			break;
+	}
+
 	if (ret == -ENODEV || ret == -ETIMEDOUT) {
 		mutex_unlock(&dev->phy_mutex);
 		return ret;
@@ -596,21 +616,28 @@ 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;
+	int i;
 
 	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 {
+	for (i = 0; i < 30; ++i) {
 		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));
+		if (ret == -ENODEV)
+			break;
+		else if (ret < 0)
+			continue;
+		else if (smsr & AX_HOST_EN)
+			break;
+	}
+
 	if (ret == -ENODEV) {
 		mutex_unlock(&dev->phy_mutex);
 		return;
-- 
2.32.0