[PATCH 6.1 074/131] net: usb: dm9601: fix uninitialized variable use in dm9601_mdio_read

Greg Kroah-Hartman
2023-10-16T09:00:06Z

From: Javier Carrasco <javier.carrasco.cruz@gmail.com>

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@vger.kernel.org
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Reported-and-tested-by: syzbot+1f53a30781af65d2c955@syzkaller.appspotmail.com
Acked-by: Peter Korsgaard <peter@korsgaard.com>
Fixes: d0374f4f9c35cdfbee0 ("USB: Davicom DM9601 usbnet driver")
Link: https://lore.kernel.org/r/20231009-topic-dm9601_uninit_mdio_read-v2-1-f2fe39739b6c@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
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
@@ -222,13 +222,18 @@ 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",