linux-kernel - [PATCH] net: usb: dm9601: fix wrong return value in dm9601_mdio

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Message-Id: <20240225-dm9601_ret_err-v1-1-02c1d959ea59@gmail.com>
Date: Sun, 25 Feb 2024 00:20:06 +0100
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>
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 wrong return value in
 dm9601_mdio_read

The MII code does not check the return value of mdio_read (among
others), and therefore no error code should be sent. A previous fix to
the use of an uninitialized variable propagates negative error codes,
that might lead to wrong operations by the MII library.

An example of such issues is the use of mii_nway_restart by the dm9601
driver. The mii_nway_restart function does not check the value returned
by mdio_read, which in this case might be a negative number which could
contain the exact bit the function checks (BMCR_ANENABLE = 0x1000).

Return zero in case of error, as it is common practice in users of
mdio_read to avoid wrong uses of the return value.

Fixes: 8f8abb863fa5 ("net: usb: dm9601: fix uninitialized variable use in dm9601_mdio_read")
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@...il.com>
---
 drivers/net/usb/dm9601.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/usb/dm9601.c b/drivers/net/usb/dm9601.c
index 99ec1d4a972d..8b6d6a1b3c2e 100644
--- a/drivers/net/usb/dm9601.c
+++ b/drivers/net/usb/dm9601.c
@@ -232,7 +232,7 @@ static int dm9601_mdio_read(struct net_device *netdev, int phy_id, int loc)
 	err = dm_read_shared_word(dev, 1, loc, &res);
 	if (err < 0) {
 		netdev_err(dev->net, "MDIO read error: %d\n", err);
-		return err;
+		return 0;
 	}

 	netdev_dbg(dev->net,

---
base-commit: 6613476e225e090cc9aad49be7fa504e290dd33d
change-id: 20240224-dm9601_ret_err-0a9c9d95cd10

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