netdev - Re: [RFC PATCH v3 3/5] Add ndo_hwtstamp_get/set support to vlan code path

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Message-ID: <ZDFylh_DM8XpmZM8@localhost>
Date:   Sat, 8 Apr 2023 15:56:38 +0200
From:   Richard Cochran <richardcochran@...il.com>
To:     Max Georgiev <glipus@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Vladimir Oltean <vladimir.oltean@....com>,
        kory.maincent@...tlin.com, netdev@...r.kernel.org,
        maxime.chevallier@...tlin.com, vadim.fedorenko@...ux.dev,
        gerhard@...leder-embedded.com
Subject: Re: [RFC PATCH v3 3/5] Add ndo_hwtstamp_get/set support to vlan code
 path

On Thu, Apr 06, 2023 at 12:21:37AM -0600, Max Georgiev wrote:

> It looks like there is a possibility that the returned hwtstamp_config structure
> will be copied twice to ifr and copied once from ifr on the return path
> in case if the underlying driver does not implement ndo_hwtstamp_get():
> - the underlying driver calls copy_to_user() inside its ndo_eth_ioctl()
>   implementation to return the data to generic_hwtstamp_get_lower();
> - then generic_hwtstamp_get_lower() calls copy_from_user() to copy it
>   back out of the ifr to kernel_hwtstamp_config structure;
> - then dev_get_hwtstamp() calls copy_to_user() again to update
>   the same ifr with the same data the ifr already contains.
> 
> Should we consider this acceptable?

This is a slow path so copying a small structure is not a concern.

Thanks,
Richard