Subject: Re: [PATCH] IPv6: Add 'autoconf' and 'disable_ipv6' module parameters

From: Vlad Yasevich <[email-masked]>
Date: Wed, 25 Mar 2009 08:36:03 -0400

Oh,  and another issue I just figured out this morning...

Vlad Yasevich wrote:
> Brian Haley wrote:
>> This is the quick and easy patch to add autoconf and
>> disable_ipv6 module parameters to IPv6.  I don't think anything
>> more complicated is needed, assuming you play with the /etc
>> configuration files.
>>
>> For example, if you wanted to enable IPv6 just on 'lo' you
>> would:
>>
>> 1. Add "ipv6" to /etc/modules (if you don't, step #3 might fail)
>>
>> 2. Add this to /etc/modprobe.conf:
>>
>> 	options ipv6 disable_ipv6=1
>>
>> 3. Add these to /etc/sysctl.conf:
>>
>> 	net.ipv6.conf.all.disable_ipv6=0
>> 	net.ipv6.conf.lo.disable_ipv6=0
> 
> This is kind of confusing.  First you say, disable IPv6, then you say enable IPv6, but
> nothing happens.  Unless you typo-ed the 'all.disable_ipv6 = 0'...
> 
> Also, it looks like if someone decides to switch IPv6 back on for a particular
> interface, they would have to wait until the next RA to get an address.  Not an
> optimum solution.
> 
>> # ip -6 a
>> 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 
>>     inet6 ::1/128 scope host 
>>        valid_lft forever preferred_lft forever
>>
>> The wording can probably be cleaned-up a little in ipv6.txt,
>> comments welcome.
>>
>>
>> ---------------------------------------------------------------
>>
>> Add 'autoconf' and 'disable_ipv6' parameters to the IPv6 module.
>>
>> The first controls if IPv6 addresses are autoconfigured from
>> prefixes received in Router Advertisements.  The IPv6 loopback
>> (::1) and link-local addresses are still configured.

You are letting link-locals to autoconfigure, but did not correctly
finish DAD, because once you set disable_ipv6, ip6_output and ipv6_rcv
will drop all IPv6 packets.

Then later, when you re-enable IPv6, you will not run DAD because the
interface will think that it's already finished.

So there is a possibility of duplicates not being detected.

-vlad

>>
>> The second controls if IPv6 addresses are desired at all.  No
>> IPv6 addresses will be added to any interfaces.
>>
>> Signed-off-by: Brian Haley <[email-masked]>
>> ---
>>  Documentation/networking/ipv6.txt |   37 +++++++++++++++++++++++++++++++++++++
>>  include/linux/ipv6.h              |    6 ++++++
>>  net/ipv6/addrconf.c               |   12 +++++++++---
>>  net/ipv6/af_inet6.c               |   22 +++++++++++++++++-----
>>  4 files changed, 69 insertions(+), 8 deletions(-)
>>
>> diff --git a/Documentation/networking/ipv6.txt b/Documentation/networking/ipv6.txt
>> index 268e5c1..9fd7e21 100644
>> --- a/Documentation/networking/ipv6.txt
>> +++ b/Documentation/networking/ipv6.txt
>> @@ -33,3 +33,40 @@ disable
>>  
>>  		A reboot is required to enable IPv6.
>>  
>> +autoconf
>> +
>> +	Specifies whether to enable IPv6 address autoconfiguration
>> +	on all interfaces.  This might be used when one does not wish
>> +	for addresses to be automatically generated from prefixes
>> +	received in Router Advertisements.
>> +
>> +	The possible values and their effects are:
>> +
>> +	0
>> +		IPv6 address autoconfiguration is disabled on all interfaces.
>> +
>> +		Only the IPv6 loopback address (::1) and link-local addresses
>> +		will be added to interfaces.
>> +
>> +	1
>> +		IPv6 address autoconfiguration is enabled on all interfaces.
>> +
>> +		This is the default value.
>> +
>> +disable_ipv6
>> +
>> +	Specifies whether to disable IPv6 on all interfaces.
>> +	This might be used when no IPv6 addresses are desired.
>> +
>> +	The possible values and their effects are:
>> +
>> +	0
>> +		IPv6 is enabled on all interfaces.
>> +
>> +		This is the default value.
>> +
>> +	1
>> +		IPv6 is disabled on all interfaces.
>> +
>> +		No IPv6 addresses will be added to interfaces.
>> +
>> diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
>> index 476d946..c662efa 100644
>> --- a/include/linux/ipv6.h
>> +++ b/include/linux/ipv6.h
>> @@ -169,6 +169,12 @@ struct ipv6_devconf {
>>  	__s32		accept_dad;
>>  	void		*sysctl;
>>  };
>> +
>> +struct ipv6_params {
>> +	__s32 disable_ipv6;
>> +	__s32 autoconf;
>> +};
>> +extern struct ipv6_params ipv6_defaults;
>>  #endif
>>  
>>  /* index values for the variables in ipv6_devconf */
>> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
>> index 8499da9..da6f01e 100644
>> --- a/net/ipv6/addrconf.c
>> +++ b/net/ipv6/addrconf.c
>> @@ -1784,6 +1784,7 @@ void addrconf_prefix_rcv(struct net_device *dev, u8 *opt, int len)
>>  	__u32 prefered_lft;
>>  	int addr_type;
>>  	struct inet6_dev *in6_dev;
>> +	struct net *net = dev_net(dev);
>>  
>>  	pinfo = (struct prefix_info *) opt;
>>  
>> @@ -1841,7 +1842,7 @@ void addrconf_prefix_rcv(struct net_device *dev, u8 *opt, int len)
>>  		if (addrconf_finite_timeout(rt_expires))
>>  			rt_expires *= HZ;
>>  
>> -		rt = rt6_lookup(dev_net(dev), &pinfo->prefix, NULL,
>> +		rt = rt6_lookup(net, &pinfo->prefix, NULL,
>>  				dev->ifindex, 1);
>>  
>>  		if (rt && addrconf_is_prefix_route(rt)) {
>> @@ -1874,11 +1875,11 @@ void addrconf_prefix_rcv(struct net_device *dev, u8 *opt, int len)
>>  
>>  	/* Try to figure out our local address for this prefix */
>>  
>> -	if (pinfo->autoconf && in6_dev->cnf.autoconf) {
>> +	if (pinfo->autoconf && in6_dev->cnf.autoconf &&
>> +	    net->ipv6.devconf_all->autoconf) {
>>  		struct inet6_ifaddr * ifp;
>>  		struct in6_addr addr;
>>  		int create = 0, update_lft = 0;
>> -		struct net *net = dev_net(dev);
>>  
>>  		if (pinfo->prefix_len == 64) {
>>  			memcpy(&addr, &pinfo->prefix, 8);
>> @@ -4378,6 +4379,11 @@ static int addrconf_init_net(struct net *net)
>>  		dflt = kmemdup(dflt, sizeof(ipv6_devconf_dflt), GFP_KERNEL);
>>  		if (dflt == NULL)
>>  			goto err_alloc_dflt;
>> +	} else {
>> +		/* these will be inherited by all namespaces */
>> +		all->autoconf = dflt->autoconf = ipv6_defaults.autoconf;
>> +		all->disable_ipv6 = dflt->disable_ipv6 =
>> +			ipv6_defaults.disable_ipv6;
> 
> Why set 'all'?  Since no interfaces are created yet, setting dflt accomplishes
> what you want.
> 
> -vlad
> 
>>  	}
>>  
>>  	net->ipv6.devconf_all = all;
>> diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
>> index fbf533c..7278dce 100644
>> --- a/net/ipv6/af_inet6.c
>> +++ b/net/ipv6/af_inet6.c
>> @@ -72,9 +72,21 @@ MODULE_LICENSE("GPL");
>>  static struct list_head inetsw6[SOCK_MAX];
>>  static DEFINE_SPINLOCK(inetsw6_lock);
>>  
>> -static int disable_ipv6 = 0;
>> -module_param_named(disable, disable_ipv6, int, 0);
>> -MODULE_PARM_DESC(disable, "Disable IPv6 such that it is non-functional");
>> +struct ipv6_params ipv6_defaults = {
>> +	.disable_ipv6 = 0,
>> +	.autoconf = 1,
>> +};
>> +
>> +static int disable_ipv6_mod = 0;
>> +
>> +module_param_named(disable, disable_ipv6_mod, int, 0444);
>> +MODULE_PARM_DESC(disable, "Disable IPv6 module such that it is non-functional");
>> +
>> +module_param_named(disable_ipv6, ipv6_defaults.disable_ipv6, int, 0444);
>> +MODULE_PARM_DESC(disable_ipv6, "Disable IPv6 on all interfaces");
>> +
>> +module_param_named(autoconf, ipv6_defaults.autoconf, int, 0444);
>> +MODULE_PARM_DESC(autoconf, "Enable IPv6 address autoconfiguration on all interfaces");
>>  
>>  static __inline__ struct ipv6_pinfo *inet6_sk_generic(struct sock *sk)
>>  {
>> @@ -1013,7 +1025,7 @@ static int __init inet6_init(void)
>>  	for(r = &inetsw6[0]; r < &inetsw6[SOCK_MAX]; ++r)
>>  		INIT_LIST_HEAD(r);
>>  
>> -	if (disable_ipv6) {
>> +	if (disable_ipv6_mod) {
>>  		printk(KERN_INFO
>>  		       "IPv6: Loaded, but administratively disabled, "
>>  		       "reboot required to enable\n");
>> @@ -1202,7 +1214,7 @@ module_init(inet6_init);
>>  
>>  static void __exit inet6_exit(void)
>>  {
>> -	if (disable_ipv6)
>> +	if (disable_ipv6_mod)
>>  		return;
>>  
>>  	/* First of all disallow new sockets creation. */
> 
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