linux-kernel - Re: Division by zero on UP (was: Re: netfilter: nat: use keyed locks)

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Message-ID: <CAMuHMdWnzu9v_arbovZV46kjrTTpVa-GQFKx+QzxU2Kpnt5itA@mail.gmail.com>
Date:   Sun, 10 Sep 2017 13:34:49 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Florian Westphal <fw@...len.de>
Cc:     Pablo Neira Ayuso <pablo@...filter.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: Division by zero on UP (was: Re: netfilter: nat: use keyed locks)

Hi Florian,

On Sun, Sep 10, 2017 at 1:21 PM, Florian Westphal <fw@...len.de> wrote:
> Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>> >                 srchash = hash_by_src(net,
>> >                                       &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
>> > -               spin_lock_bh(&nf_nat_lock);
>> > +               lock = &nf_nat_locks[srchash % ARRAY_SIZE(nf_nat_locks)];
>> > +               spin_lock_bh(lock);
>>
>> If no spinlock debugging options (CONFIG_GENERIC_LOCKBREAK,
>> CONFIG_DEBUG_SPINLOCK, CONFIG_DEBUG_LOCK_ALLOC) are enabled on a UP platform
>> (e.g. m68k defconfig), arch_spinlock_t is an empty struct, and thus
>> ARRAY_SIZE(nf_nat_locks)] is zero, leading to:
>>
>>     net/netfilter/nf_nat_core.c: In function ‘nf_nat_setup_info’:
>>     net/netfilter/nf_nat_core.c:432: warning: division by zero
>
> Gah. Sorry.  This is the 2nd time I add such a bug :(
>
> Can you send a patch?  It should be enough to use CONNTRACK_LOCKS
> instead of ARRAY_SIZE(nf_nat_locks) to avoid this problem.
>
> Otherwise I will take care of this next thing monday morning.

Thanks for the suggestion, will send a patch RSN.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds