Re: [patch added to 3.12-stable] net/ipv6: add sysctl option accept_ra_min_hop_limit

[Luis Henriques <luis.henriques@canonical.com>]

Hi,

On Thu, Mar 03, 2016 at 01:10:47PM +0100, Jiri Slaby wrote:
> From: Hangbin Liu <liuhangbin@gmail.com>
> 
> This patch has been added to the 3.12 stable tree. If you have any
> objections, please let us know.
> 
> ===============
> 
> [ Upstream commit 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@gmail.com>
> Acked-by: YOSHIFUJI Hideaki <hideaki.yoshifuji@miraclelinux.com>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> Signed-off-by: Jiri Slaby <jslaby@suse.cz>
> ---
>  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 7d8dc93fe2eb..3e5b1b5466e5 100644
> --- a/Documentation/networking/ip-sysctl.txt
> +++ b/Documentation/networking/ip-sysctl.txt
> @@ -1156,6 +1156,14 @@ accept_ra_defrtr - BOOLEAN
>  	Functional default: enabled if accept_ra is enabled.
>  			    disabled if accept_ra is disabled.
>  
> +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 88c0cf0079ad..167c976554fa 100644
> --- a/include/linux/ipv6.h
> +++ b/include/linux/ipv6.h
> @@ -30,6 +30,7 @@ struct ipv6_devconf {
>  #endif
>  	__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 593b0e32d956..25955206757a 100644
> --- a/include/uapi/linux/ipv6.h
> +++ b/include/uapi/linux/ipv6.h
> @@ -163,6 +163,8 @@ enum {
>  	DEVCONF_MLDV1_UNSOLICITED_REPORT_INTERVAL,
>  	DEVCONF_MLDV2_UNSOLICITED_REPORT_INTERVAL,
>  	DEVCONF_SUPPRESS_FRAG_NDISC,
> +	DEVCONF_USE_OIF_ADDRS_ONLY,
> +	DEVCONF_ACCEPT_RA_MIN_HOP_LIMIT,

As pointed out by Yoshifuji, this will make this uapi header contain
values that are different from upstream.  The missing DEVCONF_* values
should be added here so that they become compatible with upstream kernels.
The kernel versions affected seem to be 3.12, 3.13 and 3.19.

Cheers,
--
Lu�s


>  	DEVCONF_MAX
>  };
>  
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 38540a3ed92f..6c629ffb8756 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -192,6 +192,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
>  #endif
>  	.max_addresses		= IPV6_MAX_ADDRESSES,
>  	.accept_ra_defrtr	= 1,
> +	.accept_ra_min_hop_limit= 1,
>  	.accept_ra_pinfo	= 1,
>  #ifdef CONFIG_IPV6_ROUTER_PREF
>  	.accept_ra_rtr_pref	= 1,
> @@ -230,6 +231,7 @@ static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
>  #endif
>  	.max_addresses		= IPV6_MAX_ADDRESSES,
>  	.accept_ra_defrtr	= 1,
> +	.accept_ra_min_hop_limit= 1,
>  	.accept_ra_pinfo	= 1,
>  #ifdef CONFIG_IPV6_ROUTER_PREF
>  	.accept_ra_rtr_pref	= 1,
> @@ -4150,6 +4152,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
>  #endif
>  	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;
> @@ -4908,6 +4911,13 @@ 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 fda5d95e39f4..e34a6b3520c6 100644
> --- a/net/ipv6/ndisc.c
> +++ b/net/ipv6/ndisc.c
> @@ -1190,18 +1190,16 @@ 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:
> -- 
> 2.7.2
> 
> --
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