netdev - [PATCH] net: usb: dm9601: fix uninitialized variable use in dm9601_mdio

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Message-Id: <20231009-topic-dm9601_uninit_mdio_read-v1-1-d4d775e24e3b@gmail.com>
Date: Mon, 09 Oct 2023 20:52:55 +0200
From: Javier Carrasco <javier.carrasco.cruz@...il.com>
To: Peter Korsgaard <peter@...sgaard.com>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 syzbot+1f53a30781af65d2c955@...kaller.appspotmail.com
Cc: netdev@...r.kernel.org, linux-usb@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 Javier Carrasco <javier.carrasco.cruz@...il.com>
Subject: [PATCH] net: usb: dm9601: fix uninitialized variable use in
 dm9601_mdio_read

syzbot has found an uninit-value bug triggered by the dm9601 driver [1].

This error happens because the variable res is not updated if the call
to dm_read_shared_word returns an error or if no data is read (see
__usbnet_read_cmd()). In this particular case -EPROTO was returned and
res stayed uninitialized.

This can be avoided by checking the return value of dm_read_shared_word
and returning an error if the read operation failed or no data was read.

[1] https://syzkaller.appspot.com/bug?extid=1f53a30781af65d2c955

Signed-off-by: Javier Carrasco <javier.carrasco.cruz@...il.com>
Reported-and-tested-by: syzbot+1f53a30781af65d2c955@...kaller.appspotmail.com
---
 drivers/net/usb/dm9601.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/dm9601.c b/drivers/net/usb/dm9601.c
index 48d7d278631e..e223daa93229 100644
--- a/drivers/net/usb/dm9601.c
+++ b/drivers/net/usb/dm9601.c
@@ -222,13 +222,20 @@ static int dm9601_mdio_read(struct net_device *netdev, int phy_id, int loc)
 	struct usbnet *dev = netdev_priv(netdev);

 	__le16 res;
+	int err;

 	if (phy_id) {
 		netdev_dbg(dev->net, "Only internal phy supported\n");
 		return 0;
 	}

-	dm_read_shared_word(dev, 1, loc, &res);
+	err = dm_read_shared_word(dev, 1, loc, &res);
+	if (err <= 0) {
+		if (err == 0)
+			err = -ENODATA;
+		netdev_err(dev->net, "MDIO read error: %d\n", err);
+		return err;
+	}

 	netdev_dbg(dev->net,
 		   "dm9601_mdio_read() phy_id=0x%02x, loc=0x%02x, returns=0x%04x\n",

---
base-commit: 94f6f0550c625fab1f373bb86a6669b45e9748b3
change-id: 20231009-topic-dm9601_uninit_mdio_read-a15918ffbd6f

Best regards,
-- 
Javier Carrasco <javier.carrasco.cruz@...il.com>