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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47a8f3352a0sm69034975e9.0.2025.12.15.05.53.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Dec 2025 05:53:05 -0800 (PST) Date: Mon, 15 Dec 2025 13:53:01 +0000 From: David Laight To: Florian Westphal Cc: Anders Grahn , Pablo Neira Ayuso , Jozsef Kadlecsik , Phil Sutter , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Sebastian Andrzej Siewior , Anders Grahn , linux-kernel@vger.kernel.org, netfilter-devel@vger.kernel.org, coreteam@netfilter.org, netdev@vger.kernel.org Subject: Re: [PATCH] netfilter: nft_counter: Fix reset of counters on 32bit archs Message-ID: <20251215135301.75986b89@pumpkin> In-Reply-To: References: <20251215121258.843823-1-anders.grahn@westermo.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 15 Dec 2025 13:36:11 +0100 Florian Westphal wrote: > 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") > > Signed-off-by: Anders Grahn > > --- > > include/linux/u64_stats_sync.h | 10 ++++++++++ > > net/netfilter/nft_counter.c | 4 ++-- > > 2 files changed, 12 insertions(+), 2 deletions(-) > > > > diff --git a/include/linux/u64_stats_sync.h b/include/linux/u64_stats_sync.h > > index 457879938fc1..9942d29b17e5 100644 > > --- a/include/linux/u64_stats_sync.h > > +++ b/include/linux/u64_stats_sync.h > > @@ -89,6 +89,11 @@ static inline void u64_stats_add(u64_stats_t *p, unsigned long val) > > local64_add(val, &p->v); > > } > > > > +static inline void u64_stats_sub(u64_stats_t *p, unsigned long val) > > +{ > > + local64_sub(val, &p->v); > > +} > > That still truncates val on 32bit. Maybe use "s64 val"? > It probably depends on the type of total->bytes and total->packets. The 'bytes' value will wrap 32bits quickly, so may need to be 64bit anyway. And if (elsewhere) there are this_cpu->bytes += val; total->bytes += val; pairs you can't 'undo' the adds once total->bytes has wrapped. So should any of these types be 'long' at all? I sometimes think that 'long' should be pretty much never used in the kernel because of the 32bit/64bit portability issues. But that should have been sorted over 20 years ago. Maybe M$ had it right keeping long as 32bits :-) David