Re: [PATCH 5/8] netfilter: xt_time: use time64_t

From: Pablo Neira Ayuso <pablo@netfilter.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: y2038@lists.linaro.org, Jozsef Kadlecsik <kadlec@netfilter.org>,
	Florian Westphal <fw@strlen.de>,
	"David S. Miller" <davem@davemloft.net>,
	linux-kernel@vger.kernel.org, Eric Dumazet <edumazet@google.com>,
	netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
	netdev@vger.kernel.org
Subject: Re: [PATCH 5/8] netfilter: xt_time: use time64_t
Date: Fri, 15 Nov 2019 23:43:53 +0100	[thread overview]
Message-ID: <20191115224353.hpoyzvwvawu3fq3c@salvia> (raw)
In-Reply-To: <20191108203435.112759-6-arnd@arndb.de>

On Fri, Nov 08, 2019 at 09:34:28PM +0100, Arnd Bergmann wrote:
> The current xt_time driver suffers from the y2038 overflow on 32-bit
> architectures, when the time of day calculations break.
> 
> Also, on both 32-bit and 64-bit architectures, there is a problem with
> info->date_start/stop, which is part of the user ABI and overflows in
> in 2106.
> 
> Fix the first issue by using time64_t and explicit calls to div_u64()
> and div_u64_rem(), and document the seconds issue.
> 
> The explicit 64-bit division is unfortunately slower on 32-bit
> architectures, but doing it as unsigned lets us use the optimized
> division-through-multiplication path in most configurations.  This should
> be fine, as the code already does not allow any negative time of day
> values.
> 
> Using u32 seconds values consistently would probably also work and
> be a little more efficient, but that doesn't feel right as it would
> propagate the y2106 overflow to more place rather than fewer.

Applied, thanks.