linux-kernel - Re: [PATCH] net: ethtool: Adjust exactly ETH_GSTRING

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Message-ID: <20250416110351.1dbb7173@kmaincent-XPS-13-7390>
Date: Wed, 16 Apr 2025 11:03:51 +0200
From: Kory Maincent <kory.maincent@...tlin.com>
To: Kees Cook <kees@...nel.org>
Cc: Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew+netdev@...n.ch>,
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Subject: Re: [PATCH] net: ethtool: Adjust exactly ETH_GSTRING_LEN-long stats
 to use memcpy

On Tue, 15 Apr 2025 18:02:15 -0700
Kees Cook <kees@...nel.org> wrote:

> Many drivers populate the stats buffer using C-String based APIs (e.g.
> ethtool_sprintf() and ethtool_puts()), usually when building up the
> list of stats individually (i.e. with a for() loop). This, however,
> requires that the source strings be populated in such a way as to have
> a terminating NUL byte in the source.
> 
> Other drivers populate the stats buffer directly using one big memcpy()
> of an entire array of strings. No NUL termination is needed here, as the
> bytes are being directly passed through. Yet others will build up the
> stats buffer individually, but also use memcpy(). This, too, does not
> need NUL termination of the source strings.
> 
> However, there are cases where the strings that populate the
> source stats strings are exactly ETH_GSTRING_LEN long, and GCC
> 15's -Wunterminated-string-initialization option complains that the
> trailing NUL byte has been truncated. This situation is fine only if the
> driver is using the memcpy() approach. If the C-String APIs are used,
> the destination string name will have its final byte truncated by the
> required trailing NUL byte applied by the C-string API.
> 
> For drivers that are already using memcpy() but have initializers that
> truncate the NUL terminator, mark their source strings as __nonstring to
> silence the GCC warnings.

Shouldn't we move on to ethtool_cpy in these drivers too to unify the code?

Regards,
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com