netdev - [PATCH ethtool] ethtool: fix EEPROM byte write

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Date:   Fri, 19 Aug 2022 08:29:33 +0200
From:   Tomasz Moń <tomasz.mon@...lingroup.com>
To:     Michal Kubecek <mkubecek@...e.cz>
CC:     netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Krzysztof Drobiński 
        <k.drobinski@...lintechnologies.com>,
        Tomasz Moń <tomasz.mon@...lingroup.com>
Subject: [PATCH ethtool] ethtool: fix EEPROM byte write

ethtool since version 1.8 supports EEPROM byte write:
  # ethtool -E DEVNAME [ magic N ] [ offset N ] [ value N ]

ethtool 2.6.33 added EEPROM block write:
  # ethtool -E ethX [ magic N ] [ offset N ] [ length N ] [ value N ]

EEPROM block write introduced in 2.6.33 is backwards compatible, i.e.
when value is specified the length is forced to 1 (commandline length
value is ignored).

The byte write behaviour changed in ethtool 5.9 where the value write
only works when value parameter is specified together with length 1.
While byte writes to any offset other than 0, without length 1, simply
fail with "offset & length out of bounds" error message, writing value
to offset 0 basically erased whole EEPROM. That is, the provided byte
value was written at offset 0, but the rest of the EEPROM was set to 0.

Fix the issue by forcing length to 1 when value is provided.

Fixes: 923c3f51c444 ("ioctl: check presence of eeprom length argument properly")
Signed-off-by: Tomasz Moń <tomasz.mon@...lingroup.com>
---
 ethtool.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/ethtool.c b/ethtool.c
index 89613ca..b9602ce 100644
--- a/ethtool.c
+++ b/ethtool.c
@@ -3531,8 +3531,7 @@ static int do_seeprom(struct cmd_context *ctx)

 	if (seeprom_value_seen)
 		seeprom_length = 1;
-
-	if (!seeprom_length_seen)
+	else if (!seeprom_length_seen)
 		seeprom_length = drvinfo.eedump_len;

 	if (drvinfo.eedump_len < seeprom_offset + seeprom_length) {
-- 
2.25.1