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Date: Wed, 29 Jul 2015 19:32:07 +0900
From: YOSHIFUJI Hideaki <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: [PATCH] net/ipv6: add sysctl option min_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
> 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 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>
> ---
> Documentation/networking/ip-sysctl.txt | 4 ++++
> include/linux/ipv6.h | 1 +
> include/uapi/linux/ipv6.h | 1 +
> net/ipv6/addrconf.c | 10 ++++++++++
> net/ipv6/ndisc.c | 8 +++-----
> 5 files changed, 19 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
> index 5fae770..844904b 100644
> --- a/Documentation/networking/ip-sysctl.txt
> +++ b/Documentation/networking/ip-sysctl.txt
> @@ -1431,6 +1431,10 @@ hop_limit - INTEGER
> Default Hop Limit to set.
> Default: 64
>
> +min_hop_limit - INTEGER
> + Minimum hop limit value can be accepted from Router Advertisement.
> + Default: 1
> +
I prefer accept_ra_min_hop_limit, as we have accept_ra_rt_info_max_plen.
> mtu - INTEGER
> Default Maximum Transfer Unit
> Default: 1280 (IPv6 required minimum)
> diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
> index 82806c6..cd9e6af 100644
> --- a/include/linux/ipv6.h
> +++ b/include/linux/ipv6.h
> @@ -11,6 +11,7 @@
> struct ipv6_devconf {
> __s32 forwarding;
> __s32 hop_limit;
> + __s32 min_hop_limit;
> __s32 mtu6;
> __s32 accept_ra;
> __s32 accept_redirects;
> diff --git a/include/uapi/linux/ipv6.h b/include/uapi/linux/ipv6.h
> index 5efa54a..c1c09bb 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_MIN_HOP_LIMIT,
> DEVCONF_MAX
> };
>
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 21c2c81..b6ed39e 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -176,6 +176,7 @@ static bool ipv6_chk_same_addr(struct net *net, const struct in6_addr *addr,
> static struct ipv6_devconf ipv6_devconf __read_mostly = {
> .forwarding = 0,
> .hop_limit = IPV6_DEFAULT_HOPLIMIT,
> + .min_hop_limit = 1,
> .mtu6 = IPV6_MIN_MTU,
> .accept_ra = 1,
> .accept_redirects = 1,
> @@ -217,6 +218,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
> static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
> .forwarding = 0,
> .hop_limit = IPV6_DEFAULT_HOPLIMIT,
> + .min_hop_limit = 1,
> .mtu6 = IPV6_MIN_MTU,
> .accept_ra = 1,
> .accept_redirects = 1,
> @@ -4538,6 +4540,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
> memset(array, 0, bytes);
> array[DEVCONF_FORWARDING] = cnf->forwarding;
> array[DEVCONF_HOPLIMIT] = cnf->hop_limit;
> + array[DEVCONF_MIN_HOP_LIMIT] = cnf->min_hop_limit;
> array[DEVCONF_MTU6] = cnf->mtu6;
> array[DEVCONF_ACCEPT_RA] = cnf->accept_ra;
> array[DEVCONF_ACCEPT_REDIRECTS] = cnf->accept_redirects;
> @@ -5328,6 +5331,13 @@ static struct addrconf_sysctl_table
> .proc_handler = proc_dointvec,
> },
> {
> + .procname = "min_hop_limit",
> + .data = &ipv6_devconf.min_hop_limit,
> + .maxlen = sizeof(int),
> + .mode = 0644,
> + .proc_handler = proc_dointvec,
> + },
> + {
> .procname = "mtu",
> .data = &ipv6_devconf.mtu6,
> .maxlen = sizeof(int),
> diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
> index 0a05b35..c22f3ac 100644
> --- a/net/ipv6/ndisc.c
> +++ b/net/ipv6/ndisc.c
> @@ -1226,13 +1226,11 @@ 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.min_hop_limit <= ra_msg->icmph.icmp6_hop_limit &&
> + ra_msg->icmph.icmp6_hop_limit != 0) {
> 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");
> + ND_PRINTK(2, warn, "RA: Got route advertisement with lower hop_limit than minimum\n");
> }
ra_msg->icmph.icmp6_hop_limit != 0 is checkd by outer "if".
You do not need to update cnf.hop_limit if it is already equal to
hop limit received.
How about ignoring hop limit without message is configured value is
larger than 255, BTW?
> if (rt)
> dst_metric_set(&rt->dst, RTAX_HOPLIMIT,
>
This can be inside the inner "if".
--
Hideaki Yoshifuji <hideaki.yoshifuji@...aclelinux.com>
Technical Division, MIRACLE LINUX CORPORATION
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