netdev - Re: [PATCH net-next] ethtool: Clarify len/n

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Message-ID: <8d5e3870-1918-4071-8442-1f7328b71a75@nvidia.com>
Date: Wed, 7 Jan 2026 10:51:46 +0200
From: Gal Pressman <gal@...dia.com>
To: Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Andrew Lunn <andrew+netdev@...n.ch>,
 netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
 Simon Horman <horms@...nel.org>, Dragos Tatulea <dtatulea@...dia.com>
Subject: Re: [PATCH net-next] ethtool: Clarify len/n_stats fields in/out
 semantics

On 07/01/2026 3:48, Jakub Kicinski wrote:
> On Mon, 5 Jan 2026 18:39:23 +0200 Gal Pressman wrote:
>> - * @n_stats: On return, the number of statistics
>> + * @n_stats: On entry, the number of stats requested.
>> +	On return, the number of stats returned.
>>   * @data: Array of statistics
> 
> Missing a '*'

Ah, missed it, thanks!

> But stepping back we should rephrase the comment to cover both
> directions instead of mechanically adding the corresponding "On entry"

What do you mean?
How would you phrase it?

> 
> FTR my recollection was that we never validated these field on entry and
> if that's the case 7b07be1ff1cb6 is quite questionable, uAPI-breakage
> wise.

Can you describe the breakage please?

The kernel didn't look at this field on entry, but AFAICT, it was passed
from userspace since the beginning of time.

As a precaution, the cited patch only looks at the input values if
they're different than zero, so theoretical apps that didn't fill them
shouldn't be affected.

Maybe if the app deliberately put a wrong length value on the input buffer?