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

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Date:   Fri, 13 Aug 2021 19:01:08 +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] 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-and-tested-by: syzbot+a631ec9e717fb0423053@...kaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@...il.com>
---
 drivers/net/usb/asix_common.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/asix_common.c b/drivers/net/usb/asix_common.c
index ac92bc52a85e..572ca3077f8f 100644
--- a/drivers/net/usb/asix_common.c
+++ b/drivers/net/usb/asix_common.c
@@ -479,7 +479,13 @@ int asix_mdio_read(struct net_device *netdev, int phy_id, int loc)
 		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) {
+			++i;
+			continue;
+		}
+	} while (!(smsr & AX_HOST_EN) && (i++ < 30));
 	if (ret == -ENODEV || ret == -ETIMEDOUT) {
 		mutex_unlock(&dev->phy_mutex);
 		return ret;
-- 
2.32.0