netdev - Re: [patch] netfilter: prevent harmless integer overflow

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Date:	Thu, 20 Jun 2013 12:23:52 +0200
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	Bart De Schuymer <bart.de.schuymer@...dora.be>,
	Patrick McHardy <kaber@...sh.net>,
	Stephen Hemminger <stephen@...workplumber.org>,
	"David S. Miller" <davem@...emloft.net>,
	netfilter-devel@...r.kernel.org, netfilter@...r.kernel.org,
	coreteam@...filter.org, bridge@...ts.linux-foundation.org,
	netdev@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [patch] netfilter: prevent harmless integer overflow

On Tue, Jun 18, 2013 at 10:46:03AM +0300, Dan Carpenter wrote:
> This overflow is harmless because a few lines later we check:
> 
> 	if (num_counters != t->private->nentries) {
> 
> But it still upsets the static checkers.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> 
> diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
> index 3d110c4..141350e 100644
> --- a/net/bridge/netfilter/ebtables.c
> +++ b/net/bridge/netfilter/ebtables.c
> @@ -1278,6 +1278,8 @@ static int do_update_counters(struct net *net, const char *name,
>  
>  	if (num_counters == 0)
>  		return -EINVAL;
> +	if (num_counters > INT_MAX / sizeof(*tmp))
> +		return -ENOMEM;

This is artificially limiting to INT_MAX / sizeof(struct counters).
Before this patch, the limit is UINT_MAX / sizeof(struct counters). I
think it's very unlikely to hit such a limit though, but as you
mentioned we cover the overflow already. Adding it to calm down a
static checker sound a bit too much for me.
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