Subject: Re: [RFC PATCH v2 net-next] net: ipv6: Add a sysctl to make optimistic addresses useful candidates

From: Hannes Frederic Sowa <[email-masked]>
Date: Tue, 21 Oct 2014 21:45:43 +0200

Hi,

On Di, 2014-10-21 at 13:05 +0900, Erik Kline wrote:
> Add a sysctl that causes an interface's optimistic addresses
> to be considered equivalent to other non-deprecated addresses
> for source address selection purposes.  Preferred addresses
> will still take precedence over optimistic addresses, subject
> to other ranking in the source address selection algorithm.
> 
> This is useful where different interfaces are connected to
> different networks from different ISPs (e.g., a cell network
> and a home wifi network).
> 
> The current behaviour complies with RFC 3484/6724, and it
> makes sense if the host has only one interface, or has
> multiple interfaces on the same network (same or cooperating
> administrative domain(s), but not in the multiple distinct
> networks case.
> 
> For example, if a mobile device has an IPv6 address on an LTE
> network and then connects to IPv6-enabled wifi, while the wifi
> IPv6 address is undergoing DAD, IPv6 connections will try use
> the wifi default route with the LTE IPv6 address, and will get
> stuck until they time out.
> 
> Also, because optimistic addresses can actually be used, issue
> an RTM_NEWADDR as soon as DAD starts.  If DAD fails an separate
> RTM_DELADDR will be sent.
> 
> Also: add an entry in ip-sysctl.txt for optimistic_dad.
> 
> Signed-off-by: Erik Kline <[email-masked]>
> ---
>  Documentation/networking/ip-sysctl.txt | 13 ++++++++++++
>  include/linux/ipv6.h                   |  1 +
>  include/uapi/linux/ipv6.h              |  1 +
>  net/ipv6/addrconf.c                    | 36 ++++++++++++++++++++++++++++++++--
>  4 files changed, 49 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
> index 0307e28..e03cf49 100644
> --- a/Documentation/networking/ip-sysctl.txt
> +++ b/Documentation/networking/ip-sysctl.txt
> @@ -1452,6 +1452,19 @@ suppress_frag_ndisc - INTEGER
>  	1 - (default) discard fragmented neighbor discovery packets
>  	0 - allow fragmented neighbor discovery packets
>  
> +optimistic_dad - BOOLEAN
> +	Whether to perform Optimistic Duplicate Address Detection (RFC 4429).
> +		0: disabled (default)
> +		1: enabled
> +
> +use_optimistic - BOOLEAN
> +	If enabled, do not classify optimistic addresses as deprecated during
> +	source address selection.  Preferred addresses will still be chosen
> +	before optimistic addresses, subject to other ranking in the source
> +	address selection algorithm.
> +		0: disabled (default)
> +		1: enabled
> +
>  icmp/*:
>  ratelimit - INTEGER
>  	Limit the maximal rates for sending ICMPv6 packets.
> diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
> index ff56053..7121a2e 100644
> --- a/include/linux/ipv6.h
> +++ b/include/linux/ipv6.h
> @@ -42,6 +42,7 @@ struct ipv6_devconf {
>  	__s32		accept_ra_from_local;
>  #ifdef CONFIG_IPV6_OPTIMISTIC_DAD
>  	__s32		optimistic_dad;
> +	__s32		use_optimistic;
>  #endif
>  #ifdef CONFIG_IPV6_MROUTE
>  	__s32		mc_forwarding;
> diff --git a/include/uapi/linux/ipv6.h b/include/uapi/linux/ipv6.h
> index efa2666..e863d08 100644
> --- a/include/uapi/linux/ipv6.h
> +++ b/include/uapi/linux/ipv6.h
> @@ -164,6 +164,7 @@ enum {
>  	DEVCONF_MLDV2_UNSOLICITED_REPORT_INTERVAL,
>  	DEVCONF_SUPPRESS_FRAG_NDISC,
>  	DEVCONF_ACCEPT_RA_FROM_LOCAL,
> +	DEVCONF_USE_OPTIMISTIC,
>  	DEVCONF_MAX
>  };
>  
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 725c763..c2fddb7 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -1169,6 +1169,9 @@ enum {
>  	IPV6_SADDR_RULE_LABEL,
>  	IPV6_SADDR_RULE_PRIVACY,
>  	IPV6_SADDR_RULE_ORCHID,
> +#ifdef CONFIG_IPV6_OPTIMISTIC_DAD
> +	IPV6_SADDR_RULE_NOT_OPTIMISTIC,
> +#endif
>  	IPV6_SADDR_RULE_PREFIX,
>  	IPV6_SADDR_RULE_MAX
>  };
> @@ -1257,10 +1260,17 @@ static int ipv6_get_saddr_eval(struct net *net,
>  		score->scopedist = ret;
>  		break;
>  	case IPV6_SADDR_RULE_PREFERRED:
> +	    {
>  		/* Rule 3: Avoid deprecated and optimistic addresses */
> +		u8 avoid = IFA_F_DEPRECATED;
> +#ifdef CONFIG_IPV6_OPTIMISTIC_DAD
> +		if (!score->ifa->idev->cnf.use_optimistic)
> +			avoid |= IFA_F_OPTIMISTIC;
> +#endif
>  		ret = ipv6_saddr_preferred(score->addr_type) ||
> -		      !(score->ifa->flags & (IFA_F_DEPRECATED|IFA_F_OPTIMISTIC));
> +		      !(score->ifa->flags & avoid);
>  		break;
> +	    }
>  #ifdef CONFIG_IPV6_MIP6
>  	case IPV6_SADDR_RULE_HOA:
>  	    {
> @@ -1299,6 +1309,14 @@ static int ipv6_get_saddr_eval(struct net *net,
>  		ret = !(ipv6_addr_orchid(&score->ifa->addr) ^
>  			ipv6_addr_orchid(dst->addr));
>  		break;
> +#ifdef CONFIG_IPV6_OPTIMISTIC_DAD
> +	case IPV6_SADDR_RULE_NOT_OPTIMISTIC:
> +		/* Optimistic addresses still have lower precedence than other
> +		 * preferred addresses.
> +		 */
> +		ret = !(score->ifa->flags & IFA_F_OPTIMISTIC);
> +		break;
> +#endif

I wonder a bit why this rule is not directly ordered after
IPV6_SADDR_RULE_PREFERRED? This would e.g. matter for privacy addresses.

>  	case IPV6_SADDR_RULE_PREFIX:
>  		/* Rule 8: Use longest matching prefix */
>  		ret = ipv6_addr_diff(&score->ifa->addr, dst->addr);
> @@ -3222,8 +3240,13 @@ static void addrconf_dad_begin(struct inet6_ifaddr *ifp)
>  	 * Optimistic nodes can start receiving
>  	 * Frames right away
>  	 */
> -	if (ifp->flags & IFA_F_OPTIMISTIC)
> +	if (ifp->flags & IFA_F_OPTIMISTIC) {
>  		ip6_ins_rt(ifp->rt);
> +		/* Because optimistic nodes can receive frames, notify
> +		 * listeners. If DAD fails, RTM_DELADDR is sent.
> +		 */
> +		ipv6_ifa_notify(RTM_NEWADDR, ifp);
> +	}

I wonder if we can now delete the ipv6_ifa_notify(RTM_NEWADDR, ifp) in
addrconf_dad_completed.

>  	addrconf_dad_kick(ifp);
>  out:
> @@ -4330,6 +4353,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
>  	array[DEVCONF_ACCEPT_SOURCE_ROUTE] = cnf->accept_source_route;
>  #ifdef CONFIG_IPV6_OPTIMISTIC_DAD
>  	array[DEVCONF_OPTIMISTIC_DAD] = cnf->optimistic_dad;
> +	array[DEVCONF_USE_OPTIMISTIC] = cnf->use_optimistic;
>  #endif
>  #ifdef CONFIG_IPV6_MROUTE
>  	array[DEVCONF_MC_FORWARDING] = cnf->mc_forwarding;
> @@ -5155,6 +5179,14 @@ static struct addrconf_sysctl_table
>  			.proc_handler   = proc_dointvec,
>  
>  		},
> +		{
> +			.procname       = "use_optimistic",
> +			.data           = &ipv6_devconf.use_optimistic,
> +			.maxlen         = sizeof(int),
> +			.mode           = 0644,
> +			.proc_handler   = proc_dointvec,
> +
> +		},
>  #endif
>  #ifdef CONFIG_IPV6_MROUTE
>  		{

Otherwise looks good.

Thanks,
Hannes