[PATCH] net: usb: lan78xx: Fix lost EEPROM write timeout error(-ETIMEDOUT) in lan78xx_write_raw_eeprom

Bhanu Seshu Kumar Valluri
2025-10-09T05:30:32Z

The function lan78xx_write_raw_eeprom failed to properly propagate EEPROM
write timeout errors (-ETIMEDOUT). In the timeout fallthrough path, it first
attempted to restore the pin configuration for LED outputs and then
returned only the status of that restore operation, discarding the
original timeout error saved in ret.

As a result, callers could mistakenly treat EEPROM write operation as
successful even though the EEPROM write had actually timed out with no
or partial data write.

To fix this, handle errors in restoring the LED pin configuration separately.
If the restore succeeds, return any prior EEPROM write timeout error saved
in ret to the caller.

Suggested-by: Oleksij Rempel <o.rempel@pengutronix.de>
Fixes: 8b1b2ca83b20 ("net: usb: lan78xx: Improve error handling in EEPROM and OTP operations")
cc: stable@vger.kernel.org
Signed-off-by: Bhanu Seshu Kumar Valluri <bhanuseshukumar@gmail.com>
---
Note:
The patch is compiled and tested using EVB-LAN7800LC.
The patch was suggested by Oleksij Rempel while reviewing a fix to a bug
found by syzbot earlier.
The review mail chain where this fix was suggested is given below.
https://lore.kernel.org/all/aNzojoXK-m1Tn6Lc@pengutronix.de/

ChangeLog:
v1->v2:
Added cc:stable tag as asked during v1 review.
V1 Link : https://lore.kernel.org/all/20251004040722.82882-1-bhanuseshukumar@gmail.com/

drivers/net/usb/lan78xx.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index d75502ebbc0d..5ccbe6ae2ebe 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -1174,10 +1174,13 @@ static int lan78xx_write_raw_eeprom(struct lan78xx_net *dev, u32 offset,
}

write_raw_eeprom_done:
- if (dev->chipid == ID_REV_CHIP_ID_7800_)
- return lan78xx_write_reg(dev, HW_CFG, saved);
-
- return 0;
+ if (dev->chipid == ID_REV_CHIP_ID_7800_) {
+ int rc = lan78xx_write_reg(dev, HW_CFG, saved);
+ /* If USB fails, there is nothing to do */
+ if (rc < 0)
+ return rc;
+ }
+ return ret;
}

static int lan78xx_read_raw_otp(struct lan78xx_net *dev, u32 offset,
--
2.34.1