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Date: Tue, 28 Jul 2015 08:50:07 +0900
From: YOSHIFUJI Hideaki/吉藤英明
<hideaki.yoshifuji@...aclelinux.com>
To: Hangbin Liu <liuhangbin@...il.com>, netdev@...r.kernel.org
CC: hideaki.yoshifuji@...aclelinux.com,
Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [PATCHv2] net/ipv6: add sysctl option accept_ra_hop_limit
Hi,
Hangbin Liu wrote:
> Commit 6fd99094de2b ("ipv6: Don't reduce hop limit for an interface")
> disabled accept hop limit from RA if it is higher 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
> 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_hop_limit to let user choose whether accept
> hop limit info in RA.
>
How about introducing "minimum hop limit", instead?
|commit 6fd99094de2b83d1d4c8457f2c83483b2828e75a
|Author: D.S. Ljungmark <ljungmark@...io.se>
|Date: Wed Mar 25 09:28:15 2015 +0100
|
| ipv6: Don't reduce hop limit for an interface
:
| RFC 3756, Section 4.2.7, "Parameter Spoofing"
|
:
| > As an example, one possible approach to mitigate this threat is to
| > ignore very small hop limits. The nodes could implement a
| > configurable minimum hop limit, and ignore attempts to set it below
| > said limit.
--yoshfuji
> Signed-off-by: Hangbin Liu <liuhangbin@...il.com>
> ---
> Documentation/networking/ip-sysctl.txt | 11 +++++++++++
> include/linux/ipv6.h | 1 +
> include/uapi/linux/ipv6.h | 1 +
> net/ipv6/addrconf.c | 10 ++++++++++
> net/ipv6/ndisc.c | 17 +++++++++++------
> 5 files changed, 34 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
> index 5fae770..778c479 100644
> --- a/Documentation/networking/ip-sysctl.txt
> +++ b/Documentation/networking/ip-sysctl.txt
> @@ -1346,6 +1346,17 @@ accept_ra_pinfo - BOOLEAN
> Functional default: enabled if accept_ra is enabled.
> disabled if accept_ra is disabled.
>
> +accept_ra_hop_limit - INTEGER
> + Learn hop limit in Router Advertisement.
> +
> + Possible values are:
> + 0 Do not accept hop limit in Router Advertisements.
> + 1 Accept hop limit in Router Advertisements if it is higher
> + than the current hop limit.
> + 2 Accept hop limit in Router Advertisements anyway.
> +
> + Default: 1
> +
> accept_ra_rt_info_max_plen - INTEGER
> Maximum prefix length of Route Information in RA.
>
> diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
> index 82806c6..a21a9c6 100644
> --- a/include/linux/ipv6.h
> +++ b/include/linux/ipv6.h
> @@ -30,6 +30,7 @@ struct ipv6_devconf {
> __s32 max_addresses;
> __s32 accept_ra_defrtr;
> __s32 accept_ra_pinfo;
> + __s32 accept_ra_hop_limit;
> #ifdef CONFIG_IPV6_ROUTER_PREF
> __s32 accept_ra_rtr_pref;
> __s32 rtr_probe_interval;
> diff --git a/include/uapi/linux/ipv6.h b/include/uapi/linux/ipv6.h
> index 5efa54a..a8c1083 100644
> --- a/include/uapi/linux/ipv6.h
> +++ b/include/uapi/linux/ipv6.h
> @@ -171,6 +171,7 @@ enum {
> DEVCONF_USE_OPTIMISTIC,
> DEVCONF_ACCEPT_RA_MTU,
> DEVCONF_STABLE_SECRET,
> + DEVCONF_ACCEPT_RA_HOP_LIMIT,
> DEVCONF_MAX
> };
>
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 21c2c81..486a7a5 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -196,6 +196,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
> .accept_ra_defrtr = 1,
> .accept_ra_from_local = 0,
> .accept_ra_pinfo = 1,
> + .accept_ra_hop_limit = 1,
> #ifdef CONFIG_IPV6_ROUTER_PREF
> .accept_ra_rtr_pref = 1,
> .rtr_probe_interval = 60 * HZ,
> @@ -237,6 +238,7 @@ static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
> .accept_ra_defrtr = 1,
> .accept_ra_from_local = 0,
> .accept_ra_pinfo = 1,
> + .accept_ra_hop_limit = 1,
> #ifdef CONFIG_IPV6_ROUTER_PREF
> .accept_ra_rtr_pref = 1,
> .rtr_probe_interval = 60 * HZ,
> @@ -4561,6 +4563,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
> array[DEVCONF_MAX_ADDRESSES] = cnf->max_addresses;
> array[DEVCONF_ACCEPT_RA_DEFRTR] = cnf->accept_ra_defrtr;
> array[DEVCONF_ACCEPT_RA_PINFO] = cnf->accept_ra_pinfo;
> + array[DEVCONF_ACCEPT_RA_HOP_LIMIT] = cnf->accept_ra_hop_limit;
> #ifdef CONFIG_IPV6_ROUTER_PREF
> array[DEVCONF_ACCEPT_RA_RTR_PREF] = cnf->accept_ra_rtr_pref;
> array[DEVCONF_RTR_PROBE_INTERVAL] =
> @@ -5462,6 +5465,13 @@ static struct addrconf_sysctl_table
> .mode = 0644,
> .proc_handler = proc_dointvec,
> },
> + {
> + .procname = "accept_ra_hop_limit",
> + .data = &ipv6_devconf.accept_ra_hop_limit,
> + .maxlen = sizeof(int),
> + .mode = 0644,
> + .proc_handler = proc_dointvec,
> + },
> #ifdef CONFIG_IPV6_ROUTER_PREF
> {
> .procname = "accept_ra_rtr_pref",
> diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
> index 0a05b35..aca67da 100644
> --- a/net/ipv6/ndisc.c
> +++ b/net/ipv6/ndisc.c
> @@ -1226,13 +1226,18 @@ 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) {
> + switch (in6_dev->cnf.accept_ra_hop_limit) {
> + case 0:
> + break;
> + case 1:
> + if (in6_dev->cnf.hop_limit > ra_msg->icmph.icmp6_hop_limit) {
> + ND_PRINTK(2, warn,
> + "RA: Got route advertisement with lower hop_limit than current\n");
> + break;
> + }
> + default:
> in6_dev->cnf.hop_limit = ra_msg->icmph.icmp6_hop_limit;
> - } else {
> - ND_PRINTK(2, warn, "RA: Got route advertisement with lower hop_limit than current\n");
> + break;
> }
> if (rt)
> dst_metric_set(&rt->dst, RTAX_HOPLIMIT,
>
--
吉藤英明 <hideaki.yoshifuji@...aclelinux.com>
ミラクル・リナックス株式会社 技術本部 サポート部
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