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

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Message-ID: <20220819082717.5w36vkp4jnsbdisg@lion.mk-sys.cz>
Date:   Fri, 19 Aug 2022 10:27:17 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Tomasz Moń <tomasz.mon@...lingroup.com>
Cc:     netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Krzysztof Drobiński 
        <k.drobinski@...lintechnologies.com>
Subject: Re: [PATCH ethtool] ethtool: fix EEPROM byte write

On Fri, Aug 19, 2022 at 08:29:33AM +0200, Tomasz Moń wrote:
> 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) {

I don't like the idea of silently ignoring the length parameter if value
is used. We should rather issue an error for invalid combination of
parameters, i.e. value present and length different from 1.

Michal

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