[PATCH AUTOSEL 6.11 075/244] net: phy: Check for read errors in SIOCGMIIREG

[Sasha Levin]

From: Niklas Söderlund <niklas.soderlund+renesas@xxxxxxxxxxxx>

[ Upstream commit 569bf6d481b0b823c3c9c3b8be77908fd7caf66b ]

When reading registers from the PHY using the SIOCGMIIREG IOCTL any
errors returned from either mdiobus_read() or mdiobus_c45_read() are
ignored, and parts of the returned error is passed as the register value
back to user-space.

For example, if mdiobus_c45_read() is used with a bus that do not
implement the read_c45() callback -EOPNOTSUPP is returned. This is
however directly stored in mii_data->val_out and returned as the
registers content. As val_out is a u16 the error code is truncated and
returned as a plausible register value.

Fix this by first checking the return value for errors before returning
it as the register content.

Before this patch,

    # phytool read eth0/0:1/0
    0xffa1

After this change,

    $ phytool read eth0/0:1/0
    error: phy_read (-95)

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@xxxxxxxxxxxx>
Reviewed-by: Florian Fainelli <florian.fainelli@xxxxxxxxxxxx>
Reviewed-by: Andrew Lunn <andrew@xxxxxxx>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
Reviewed-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
Link: https://patch.msgid.link/20240903171536.628930-1-niklas.soderlund+renesas@xxxxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/net/phy/phy.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
index 785182fa5fe01..b88d857ea23b8 100644
--- a/drivers/net/phy/phy.c
+++ b/drivers/net/phy/phy.c
@@ -342,14 +342,19 @@ int phy_mii_ioctl(struct phy_device *phydev, struct ifreq *ifr, int cmd)
 		if (mdio_phy_id_is_c45(mii_data->phy_id)) {
 			prtad = mdio_phy_id_prtad(mii_data->phy_id);
 			devad = mdio_phy_id_devad(mii_data->phy_id);
-			mii_data->val_out = mdiobus_c45_read(
-				phydev->mdio.bus, prtad, devad,
-				mii_data->reg_num);
+			ret = mdiobus_c45_read(phydev->mdio.bus, prtad, devad,
+					       mii_data->reg_num);
+
 		} else {
-			mii_data->val_out = mdiobus_read(
-				phydev->mdio.bus, mii_data->phy_id,
-				mii_data->reg_num);
+			ret = mdiobus_read(phydev->mdio.bus, mii_data->phy_id,
+					   mii_data->reg_num);
 		}
+
+		if (ret < 0)
+			return ret;
+
+		mii_data->val_out = ret;
+
 		return 0;
 
 	case SIOCSMIIREG:
-- 
2.43.0