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Message-ID: <56C6D736.20901@jp.fujitsu.com>
Date:	Fri, 19 Feb 2016 17:49:58 +0900
From:	Yuki Machida <machida.yuki@...fujitsu.com>
To:	netdev@...r.kernel.org, hideaki.yoshifuji@...aclelinux.com,
	yoshfuji@...ux-ipv6.org, "David S. Miller" <davem@...emloft.net>
Cc:	Hangbin Liu <liuhangbin@...il.com>
Subject: Re: [PATCH stable v2 1/1] net/ipv6: add sysctl option
 accept_ra_min_hop_limit

ping? thanks.

On 2016年02月03日 10:56, Yuki Machida wrote:
> Please apply the following patch to v4.1.x.
> 
> By commit 6fd99094de2b ("ipv6: Don't reduce hop limit for an interface")
> that have been added in the 4.0-rc7, it no longer comply with RFC4861.
> This problem has been fixed in the commit 8013d1d7eafb
> ("net/ipv6: add sysctl option accept_ra_min_hop_limit")
> in 4.3-rc1, but 4.1.x is still.
> 
> [ Upstream 8013d1d7eafb0589ca766db6b74026f76b7f5cb4 ]
> 
> Commit 6fd99094de2b ("ipv6: Don't reduce hop limit for an interface")
> disabled accept hop limit from RA if it is smaller than the current hop
> limit for security stuff. But this behavior kind of break the RFC definition.
> 
> RFC 4861, 6.3.4.  Processing Received Router Advertisements
>     A Router Advertisement field (e.g., Cur Hop Limit, Reachable Time,
>     and Retrans Timer) may contain a value denoting that it is
>     unspecified.  In such cases, the parameter should be ignored and the
>     host should continue using whatever value it is already using.
> 
>     If the received Cur Hop Limit value is non-zero, the host SHOULD set
>     its CurHopLimit variable to the received value.
> 
> So add sysctl option accept_ra_min_hop_limit to let user choose the minimum
> hop limit value they can accept from RA. And set default to 1 to meet RFC
> standards.
> 
> Signed-off-by: Hangbin Liu <liuhangbin@...il.com>
> Acked-by: YOSHIFUJI Hideaki <hideaki.yoshifuji@...aclelinux.com>
> Signed-off-by: David S. Miller <davem@...emloft.net>
> ---
>   Documentation/networking/ip-sysctl.txt |  8 ++++++++
>   include/linux/ipv6.h                   |  1 +
>   include/uapi/linux/ipv6.h              |  2 ++
>   net/ipv6/addrconf.c                    | 10 ++++++++++
>   net/ipv6/ndisc.c                       | 16 +++++++---------
>   5 files changed, 28 insertions(+), 9 deletions(-)
> 
> diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
> index 071fb18..07fad3d 100644
> --- a/Documentation/networking/ip-sysctl.txt
> +++ b/Documentation/networking/ip-sysctl.txt
> @@ -1321,6 +1321,14 @@ accept_ra_from_local - BOOLEAN
>   	   disabled if accept_ra_from_local is disabled
>                  on a specific interface.
>   
> +accept_ra_min_hop_limit - INTEGER
> +	Minimum hop limit Information in Router Advertisement.
> +
> +	Hop limit Information in Router Advertisement less than this
> +	variable shall be ignored.
> +
> +	Default: 1
> +
>   accept_ra_pinfo - BOOLEAN
>   	Learn Prefix Information in Router Advertisement.
>   
> diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
> index e4b4649..01c2592 100644
> --- a/include/linux/ipv6.h
> +++ b/include/linux/ipv6.h
> @@ -29,6 +29,7 @@ struct ipv6_devconf {
>   	__s32		max_desync_factor;
>   	__s32		max_addresses;
>   	__s32		accept_ra_defrtr;
> +	__s32		accept_ra_min_hop_limit;
>   	__s32		accept_ra_pinfo;
>   #ifdef CONFIG_IPV6_ROUTER_PREF
>   	__s32		accept_ra_rtr_pref;
> diff --git a/include/uapi/linux/ipv6.h b/include/uapi/linux/ipv6.h
> index 5efa54a..21cfddf 100644
> --- a/include/uapi/linux/ipv6.h
> +++ b/include/uapi/linux/ipv6.h
> @@ -171,6 +171,8 @@ enum {
>   	DEVCONF_USE_OPTIMISTIC,
>   	DEVCONF_ACCEPT_RA_MTU,
>   	DEVCONF_STABLE_SECRET,
> +	__DEVCONF_USE_OIF_ADDRS_ONLY,	/* not implemented */
> +	DEVCONF_ACCEPT_RA_MIN_HOP_LIMIT,
>   	DEVCONF_MAX
>   };
>   
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index f4795b0..28c4bc5 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -195,6 +195,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
>   	.max_addresses		= IPV6_MAX_ADDRESSES,
>   	.accept_ra_defrtr	= 1,
>   	.accept_ra_from_local	= 0,
> +	.accept_ra_min_hop_limit= 1,
>   	.accept_ra_pinfo	= 1,
>   #ifdef CONFIG_IPV6_ROUTER_PREF
>   	.accept_ra_rtr_pref	= 1,
> @@ -236,6 +237,7 @@ static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
>   	.max_addresses		= IPV6_MAX_ADDRESSES,
>   	.accept_ra_defrtr	= 1,
>   	.accept_ra_from_local	= 0,
> +	.accept_ra_min_hop_limit= 1,
>   	.accept_ra_pinfo	= 1,
>   #ifdef CONFIG_IPV6_ROUTER_PREF
>   	.accept_ra_rtr_pref	= 1,
> @@ -4565,6 +4567,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
>   	array[DEVCONF_MAX_DESYNC_FACTOR] = cnf->max_desync_factor;
>   	array[DEVCONF_MAX_ADDRESSES] = cnf->max_addresses;
>   	array[DEVCONF_ACCEPT_RA_DEFRTR] = cnf->accept_ra_defrtr;
> +	array[DEVCONF_ACCEPT_RA_MIN_HOP_LIMIT] = cnf->accept_ra_min_hop_limit;
>   	array[DEVCONF_ACCEPT_RA_PINFO] = cnf->accept_ra_pinfo;
>   #ifdef CONFIG_IPV6_ROUTER_PREF
>   	array[DEVCONF_ACCEPT_RA_RTR_PREF] = cnf->accept_ra_rtr_pref;
> @@ -5458,6 +5461,13 @@ static struct addrconf_sysctl_table
>   			.proc_handler	= proc_dointvec,
>   		},
>   		{
> +			.procname	= "accept_ra_min_hop_limit",
> +			.data		= &ipv6_devconf.accept_ra_min_hop_limit,
> +			.maxlen		= sizeof(int),
> +			.mode		= 0644,
> +			.proc_handler	= proc_dointvec,
> +		},
> +		{
>   			.procname	= "accept_ra_pinfo",
>   			.data		= &ipv6_devconf.accept_ra_pinfo,
>   			.maxlen		= sizeof(int),
> diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
> index 96f153c..abb0bdd 100644
> --- a/net/ipv6/ndisc.c
> +++ b/net/ipv6/ndisc.c
> @@ -1225,18 +1225,16 @@ static void ndisc_router_discovery(struct sk_buff *skb)
>   
>   	if (rt)
>   		rt6_set_expires(rt, jiffies + (HZ * lifetime));
> -	if (ra_msg->icmph.icmp6_hop_limit) {
> -		/* Only set hop_limit on the interface if it is higher than
> -		 * the current hop_limit.
> -		 */
> -		if (in6_dev->cnf.hop_limit < ra_msg->icmph.icmp6_hop_limit) {
> +	if (in6_dev->cnf.accept_ra_min_hop_limit < 256 &&
> +	    ra_msg->icmph.icmp6_hop_limit) {
> +		if (in6_dev->cnf.accept_ra_min_hop_limit <= ra_msg->icmph.icmp6_hop_limit) {
>   			in6_dev->cnf.hop_limit = ra_msg->icmph.icmp6_hop_limit;
> +			if (rt)
> +				dst_metric_set(&rt->dst, RTAX_HOPLIMIT,
> +					       ra_msg->icmph.icmp6_hop_limit);
>   		} else {
> -			ND_PRINTK(2, warn, "RA: Got route advertisement with lower hop_limit than current\n");
> +			ND_PRINTK(2, warn, "RA: Got route advertisement with lower hop_limit than minimum\n");
>   		}
> -		if (rt)
> -			dst_metric_set(&rt->dst, RTAX_HOPLIMIT,
> -				       ra_msg->icmph.icmp6_hop_limit);
>   	}
>   
>   skip_defrtr:
> 

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