Subject: Re: [PATCH] devinet: sysctl setup off by one

From: Pavel Emelyanov <[email-masked]>
Date: Mon, 26 May 2008 11:39:21 +0400

Stephen Hemminger wrote:
> It look like the code to setup /proc/sys/net/ipv4/conf/XXX has an off by one bug
> that causes the last entry (arp_accept) not to be adjusted properly.  This causes
> changes to the value to occur in the default namespace not the clone? Don't use
> network namespaces myself, but this looks like a bug.
> 
> Signed-off-by: Stephen Hemminger <[email-masked]>
> 
> --- a/net/ipv4/devinet.c	2008-05-23 15:23:19.000000000 -0700
> +++ b/net/ipv4/devinet.c	2008-05-23 15:29:17.000000000 -0700
> @@ -1466,7 +1466,7 @@ static int __devinet_sysctl_register(str
>  	if (!t)
>  		goto out;
>  
> -	for (i = 0; i < ARRAY_SIZE(t->devinet_vars) - 1; i++) {
> +	for (i = 0; i < ARRAY_SIZE(t->devinet_vars); i++) {
>  		t->devinet_vars[i].data += (char *)p - (char *)&ipv4_devconf;
>  		t->devinet_vars[i].extra1 = p;
>  		t->devinet_vars[i].extra2 = net;
> 

This off-by-one is required, since the very last element of this array
is used as a sentinel, that shows sysctl engine when to stop processing 
the table.

Look, the sizeof(t->devinet_vars) is __NET_IPV4_CONF_MAX == 22, thus
entries 0, 1, ... 20 are tables and the 21-st is this sentinel, so the
initialization of this last entry, whose index is (this_sizeof() - 1),
is not required.

Thanks,
Pavel