Re: [PATCH] net: ethtool: Adjust exactly ETH_GSTRING_LEN-long stats to use memcpy

[Kees Cook <kees@kernel.org>]

On Wed, Apr 16, 2025 at 11:03:51AM +0200, Kory Maincent wrote:
> On Tue, 15 Apr 2025 18:02:15 -0700
> Kees Cook <kees@kernel.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?

I decided that the code churn wasn't worth it. Perhaps in a follow-up
patch if folks want to see the removal of the explicit memcpy() uses?

-- 
Kees Cook