[PATCH net v2] net: usb: lan78xx: reject invalid EEPROM write requests

[Stefano Munari]

The runtime PM handling removed the -EINVAL return for invalid
EEPROM/OTP write requests. These requests now return zero from a
successful usb_autopm_get_interface() call, even though no data is
written.

Set ret to -EINVAL for invalid requests while preserving the runtime
PM reference release.

Fixes: 8a7ffeb795f8 ("lan78xx: Fix for eeprom read/write when device auto suspend")
Signed-off-by: Stefano Munari <stefanomunari.sm@xxxxxxxxx>
Reviewed-by: Nicolai Buchwitz <nb@xxxxxxxxxxx>
Tested-by: Nicolai Buchwitz <nb@xxxxxxxxxxx> # Raspberry Pi 3B+ (LAN7515)
---
Changes in v2:
- Add braces to all branches of the if/else chain as suggested by Andrew.
- Add Nicolai's Reviewed-by and Tested-by tags.

v1: https://lore.kernel.org/r/20261009005702.164936-1-stefanomunari.sm@xxxxxxxxx

Tested on a Raspberry Pi 3 Model B+ with the onboard Ethernet
controller, using raspberrypi/linux commit bba53a117a4a on the
rpi-6.6.y branch as the baseline.

  ethtool -E eth0 magic 0 offset 0 length 1 value 0

The command succeeds without the patch and reports "Invalid argument"
with the patch applied.
---
 drivers/net/usb/lan78xx.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index 5655941f1478..2fed938fc7f4 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -1712,13 +1712,16 @@ static int lan78xx_ethtool_set_eeprom(struct net_device *netdev,
 	/* Invalid EEPROM_INDICATOR at offset zero will result in a failure
 	 * to load data from EEPROM
 	 */
-	if (ee->magic == LAN78XX_EEPROM_MAGIC)
+	if (ee->magic == LAN78XX_EEPROM_MAGIC) {
 		ret = lan78xx_write_raw_eeprom(dev, ee->offset, ee->len, data);
-	else if ((ee->magic == LAN78XX_OTP_MAGIC) &&
+	} else if ((ee->magic == LAN78XX_OTP_MAGIC) &&
 		 (ee->offset == 0) &&
 		 (ee->len == 512) &&
-		 (data[0] == OTP_INDICATOR_1))
+		 (data[0] == OTP_INDICATOR_1)) {
 		ret = lan78xx_write_raw_otp(dev, ee->offset, ee->len, data);
+	} else {
+		ret = -EINVAL;
+	}
 
 	usb_autopm_put_interface(dev->intf);
 
-- 
2.55.0