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

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Date: Mon, 09 Oct 2023 22:48:30 +0200
From: Peter Korsgaard <peter@...sgaard.com>
To: Javier Carrasco <javier.carrasco.cruz@...il.com>
Cc: "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,
  netdev@...r.kernel.org,  linux-usb@...r.kernel.org,
  linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: usb: dm9601: fix uninitialized variable use in
 dm9601_mdio_read

>>>>> "Javier" == Javier Carrasco <javier.carrasco.cruz@...il.com> writes:

 > 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;

Looking at dm_read(), it doesn't look like we can end up here with err
== 0, but OK.

Acked-by: Peter Korsgaard <peter@...sgaard.com>

-- 
Bye, Peter Korsgaard