linux-kernel - Re: [PATCH] netfilter: nft_counter: Fix reset of counters on 32bit archs

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Message-ID: <aUAhDdMGykBb2BOg@horms.kernel.org>
Date: Mon, 15 Dec 2025 14:54:05 +0000
From: Simon Horman <horms@...nel.org>
To: Anders Grahn <anders.grahn@...il.com>
Cc: Pablo Neira Ayuso <pablo@...filter.org>,
	Jozsef Kadlecsik <kadlec@...filter.org>,
	Florian Westphal <fw@...len.de>, Phil Sutter <phil@....cc>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Anders Grahn <anders.grahn@...termo.com>,
	linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
	coreteam@...filter.org, netdev@...r.kernel.org
Subject: Re: [PATCH] netfilter: nft_counter: Fix reset of counters on 32bit
 archs

On Mon, Dec 15, 2025 at 01:12:57PM +0100, Anders Grahn wrote:
> nft_counter_reset() calls u64_stats_add() with a negative value to reset
> the counter. This will work on 64bit archs, hence the negative value
> added will wrap as a 64bit value which then can wrap the stat counter as
> well.
> 
> On 32bit archs, the added negative value will wrap as a 32bit value and
> _not_ wrapping the stat counter properly. In most cases, this would just
> lead to a very large 32bit value being added to the stat counter.
> 
> Fix by introducing u64_stats_sub().
> 
> Fixes: 4a1d3acd6ea8 ("netfilter: nft_counter: Use u64_stats_t for statistic")

Nit: there is a minor mismatch in the subject of the Fixes tag and
     git history: the trailing '.'
     I would go for this. But perhaps it doesn't matter.

Fixes: 4a1d3acd6ea8 ("netfilter: nft_counter: Use u64_stats_t for statistic.")

> Signed-off-by: Anders Grahn <anders.grahn@...termo.com>

...