Re: [B.A.T.M.A.N.] [PATCH 1/2] batman-adv: Avoid u32 overflow during gateway select

From: Antonio Quartulli <antonio@meshcoding.com>
To: David Miller <davem@davemloft.net>
Cc: ruben@vfn-nrw.de, mareklindner@neomailbox.ch,
	netdev@vger.kernel.org, b.a.t.m.a.n@lists.open-mesh.org
Subject: Re: [B.A.T.M.A.N.] [PATCH 1/2] batman-adv: Avoid u32 overflow during gateway select
Date: Mon, 22 Jun 2015 14:53:12 +0200	[thread overview]
Message-ID: <55880538.1050109@meshcoding.com> (raw)
In-Reply-To: <1534492.Qn5WYoJSum@sven-edge>

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On 21/06/15 20:27, Sven Eckelmann wrote:
> On Sunday 21 June 2015 09:37:13 David Miller wrote:
>> From: Antonio Quartulli <antonio@meshcoding.com>
>> Date: Tue, 16 Jun 2015 21:06:23 +0200
>>
>>> @@ -133,7 +133,7 @@ batadv_gw_get_best_gw_node(struct batadv_priv
>>> *bat_priv)> 
>>>  	struct batadv_neigh_node *router;
>>>  	struct batadv_neigh_ifinfo *router_ifinfo;
>>>  	struct batadv_gw_node *gw_node, *curr_gw = NULL;
>>>
>>> -	uint32_t max_gw_factor = 0, tmp_gw_factor = 0;
>>> +	uint64_t max_gw_factor = 0, tmp_gw_factor = 0;
>>>
>>>  	uint32_t gw_divisor;
>>
>> Divides are performed using these variables, so if you make
>> them 64-bit the build will fail.  You have to use one of the
>> routines in include/linux/math64.h in this situation, but
>> realize that this operation is now going to be quite expensive.
> 
> Just a minor comment: The division is currently "max_gw_factor >> 18" which 
> the compiler also outputs as such (shrd + shr on i586). This is the reason why 
> it currently also works on architectures without a native 64 bit div.

Thanks for the comment David and Sven.

David you can drop this pull request.
I'll send a new one later with a modified patch that explicitly
introduces the shift.

Thanks!

-- 
Antonio Quartulli

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