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Date: Mon, 8 Apr 2024 09:18:29 +0100
From: Simon Horman <horms@kernel.org>
To: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
	pabeni@redhat.com, netdev@vger.kernel.org,
	aleksander.lobakin@intel.com,
	nex.sw.ncis.osdt.itp.upstreaming@intel.com,
	Arnd Bergmann <arnd@arndb.de>
Subject: Re: [net-next v2] pfcp: avoid copy warning by simplifing code
Message-ID: <20240408081829.GC26556@kernel.org>
References: <20240405063605.649744-1-michal.swiatkowski@linux.intel.com>
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In-Reply-To: <20240405063605.649744-1-michal.swiatkowski@linux.intel.com>

On Fri, Apr 05, 2024 at 08:36:05AM +0200, Michal Swiatkowski wrote:
> >From Arnd comments:
> "The memcpy() in the ip_tunnel_info_opts_set() causes
> a string.h fortification warning, with at least gcc-13:
> 
>     In function 'fortify_memcpy_chk',
>         inlined from 'ip_tunnel_info_opts_set' at include/net/ip_tunnels.h:619:3,
>         inlined from 'pfcp_encap_recv' at drivers/net/pfcp.c:84:2:
>     include/linux/fortify-string.h:553:25: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
>       553 |                         __write_overflow_field(p_size_field, size);"
> 
> It is a false-positivie caused by ambiguity of the union.
> 
> However, as Arnd noticed, copying here is unescessary. The code can be
> simplified to avoid calling ip_tunnel_info_opts_set(), which is doing
> copying, setting flags and options_len.
> 
> Set correct flags and options_len directly on tun_info.
> 
> Fixes: 6dd514f48110 ("pfcp: always set pfcp metadata")
> Reported-by: Arnd Bergmann <arnd@arndb.de>
> Closes: https://lore.kernel.org/netdev/701f8f93-f5fb-408b-822a-37a1d5c424ba@app.fastmail.com/
> Acked-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>

I agree that it's nice to avoid a copy.
But I do wonder where else this pattern may exist.
And if it might be worth introducing a helper for it.

Regardless, this looks good to me.

Reviewed-by: Simon Horman <horms@kernel.org>

...