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
higher?
> 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 <liuhang...@gmail.com>
> ---
> Documentation/networking/ip-sysctl.txt | 8 ++++++++
> include/linux/ipv6.h | 1 +
> include/uapi/linux/ipv6.h | 1 +
> net/ipv6/addrconf.c | 10 ++++++++++
> net/ipv6/ndisc.c | 14 +++++---------
> 5 files changed, 25 insertions(+), 9 deletions(-)
>
> diff --git a/Documentation/networking/ip-sysctl.txt
> b/Documentation/networking/ip-sysctl.txt
> index 1a5ab21b..00d26d9 100644
> --- a/Documentation/networking/ip-sysctl.txt
> +++ b/Documentation/networking/ip-sysctl.txt
> @@ -1340,6 +1340,14 @@ 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 06ed637..cb9dcad 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 641a146..80f3b74 100644
> --- a/include/uapi/linux/ipv6.h
> +++ b/include/uapi/linux/ipv6.h
> @@ -172,6 +172,7 @@ enum {
> DEVCONF_ACCEPT_RA_MTU,
> DEVCONF_STABLE_SECRET,
> DEVCONF_USE_OIF_ADDRS_ONLY,
> + DEVCONF_ACCEPT_RA_MIN_HOP_LIMIT,
> DEVCONF_MAX
> };
>
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index eb0c6a3..53e3a9d 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,
> @@ -237,6 +238,7 @@ 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,
> @@ -4588,6 +4590,7 @@ 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;
> @@ -5485,6 +5488,13 @@ 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 0a05b35..5619e64 100644
> --- a/net/ipv6/ndisc.c
> +++ b/net/ipv6/ndisc.c
> @@ -1225,18 +1225,14 @@ 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) {
> - 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");
> - }
> + if (in6_dev->cnf.accept_ra_min_hop_limit < 256 &&
> ra_msg->icmph.icmp6_hop_limit &&
> + 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 minimum\n");
> }
>
> skip_defrtr:
>
No because we emit incorrect warning with 0 hoplimit in RA.
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 minimum\n");
}
}
--
Hideaki Yoshifuji <hideaki.yoshif...@miraclelinux.com>
Technical Division, MIRACLE LINUX CORPORATION
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