netdev - [PATCH v2] net: asix: fix uninit value in asix_mdio

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Message-Id: <20210813224219.11359-1-paskripkin@gmail.com>
Date:   Sat, 14 Aug 2021 01:42:19 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     davem@...emloft.net, kuba@...nel.org, linux@...pel-privat.de,
        himadrispandya@...il.com, andrew@...n.ch
Cc:     linux-usb@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Pavel Skripkin <paskripkin@...il.com>,
        syzbot+a631ec9e717fb0423053@...kaller.appspotmail.com
Subject: [PATCH v2] net: asix: fix uninit value in asix_mdio_read

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 cheking and just continue the loop instead of
checking uninit value.

Fixes: 8a46f665833a ("net: asix: Avoid looping when the device is disconnected")
Reported-by: syzbot+a631ec9e717fb0423053@...kaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@...il.com>
---

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.

---
 drivers/net/usb/asix_common.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/net/usb/asix_common.c b/drivers/net/usb/asix_common.c
index ac92bc52a85e..7019c25e591c 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 i;
 	int ret;
 
 	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;
-- 
2.32.0