[PATCH 5.10 035/202] net: usb: dm9601: fix uninitialized variable use in dm9601_mdio_read

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5.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Javier Carrasco <javier.carrasco.cruz@xxxxxxxxx>

commit 8f8abb863fa5a4cc18955c6a0e17af0ded3e4a76 upstream.

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. 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 propagating the error if the read operation failed.

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

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@xxxxxxxxx>
Reported-and-tested-by: syzbot+1f53a30781af65d2c955@xxxxxxxxxxxxxxxxxxxxxxxxx
Acked-by: Peter Korsgaard <peter@xxxxxxxxxxxxx>
Fixes: d0374f4f9c35cdfbee0 ("USB: Davicom DM9601 usbnet driver")
Link: https://lore.kernel.org/r/20231009-topic-dm9601_uninit_mdio_read-v2-1-f2fe39739b6c@xxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/usb/dm9601.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/drivers/net/usb/dm9601.c
+++ b/drivers/net/usb/dm9601.c
@@ -221,13 +221,18 @@ static int dm9601_mdio_read(struct net_d
 	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) {
+		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",





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