linux-kernel - Re: [PATCH 3/5] net/netfilter/ipvs/ip_vs_ctl.c: drop argument range check just before the check for equality

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Message-ID: <alpine.LFD.2.11.1407221136420.1949@ja.home.ssi.bg>
Date:	Tue, 22 Jul 2014 11:52:02 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	Dan Carpenter <dan.carpenter@...cle.com>
cc:	Andrey Utkin <andrey.krieger.utkin@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kernel-janitors@...r.kernel.org, coreteam@...filter.org,
	netfilter-devel@...r.kernel.org, lvs-devel@...r.kernel.org,
	netdev@...r.kernel.org, dcb314@...mail.com,
	David Miller <davem@...emloft.net>, kadlec@...ckhole.kfki.hu,
	Patrick McHardy <kaber@...sh.net>, pablo@...filter.org,
	Simon Horman <horms@...ge.net.au>, wensong@...ux-vs.org
Subject: Re: [PATCH 3/5] net/netfilter/ipvs/ip_vs_ctl.c: drop argument range
 check just before the check for equality


	Hello,

On Tue, 22 Jul 2014, Dan Carpenter wrote:

> On Mon, Jul 21, 2014 at 11:01:56PM +0300, Julian Anastasov wrote:
> > @@ -2333,13 +2339,12 @@ do_ip_vs_set_ctl(struct sock *sk, int cmd, void __user *user, unsigned int len)
> >  	struct ip_vs_dest_user_kern udest;
> >  	struct netns_ipvs *ipvs = net_ipvs(net);
> >  
> > +	BUILD_BUG_ON(sizeof(arg) > 256);
> 
> 256 is off-by-one because u8 ranges from 0-255 so we are never able to
> copy 256 bytes into the "arg" buffer.

	I'll change it to >= 256, to catch that we can
not hold such big size in unsigned char [gs]et_arglen and
also as an indication that we have to use allocated buffer
instead of stack.

> > -	if (copylen > 128)
> > +	if (*len < (int) copylen || *len < 0) {
> > +		pr_err("get_ctl: len %d < %u\n", *len, copylen);
> 
> Don't let users flood dmesg.  Just return an error.  (This can be
> triggered by non-root as well).

	For now both set and get are privileged operations,
so we can keep it, it can catch if something wrong happens
with the structure sizes.

Regards

--
Julian Anastasov <ja@....bg>
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