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Date: Wed, 29 Jul 2015 22:46:52 +0800
From: Hangbin Liu <liuhangbin@...il.com>
To: YOSHIFUJI Hideaki <hideaki.yoshifuji@...aclelinux.com>
Cc: network dev <netdev@...r.kernel.org>,
Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [PATCHv3] net/ipv6: add sysctl option accept_ra_min_hop_limit
Hi Yoshifuji-san,
Please see comments in the mail.
2015-07-29 18:39 GMT+08:00 YOSHIFUJI Hideaki
<hideaki.yoshifuji@...aclelinux.com>:
> Hi,
>
> Thank you for you updated patch.
>
> 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 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>
>> ---
>> 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 | 8 +++-----
>> 5 files changed, 23 insertions(+), 5 deletions(-)
>>
>> diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
>> index 5fae770..ced0a38 100644
>> --- a/Documentation/networking/ip-sysctl.txt
>> +++ b/Documentation/networking/ip-sysctl.txt
>> @@ -1346,6 +1346,14 @@ accept_ra_pinfo - 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_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..ac01ab4 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_min_hop_limit;
>
> accept_ra_defrtr
> accept_ra_min_hop_limit
> accept_ra_pinfo
> (matter of taste)
Ah yes, alphabet order, that make sense.
>
>> #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..68094e33 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_MIN_HOP_LIMIT,
>> DEVCONF_MAX
>> };
>>
>
> This patch cannot apply to current net-next. Please rebase your patch.
Got it, I will fix the patch based on latest net-next.
>
>> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
>> index 21c2c81..77df8f2 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_min_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_min_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_MIN_HOP_LIMIT] = cnf->accept_ra_min_hop_limit;
>
> DEFRTR, MIN_HOP_LIMIT then PINFO
> (matter of taste)
OK, will fix it.
>
>> #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_min_hop_limit",
>> + .data = &ipv6_devconf.accept_ra_min_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..acda056 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.accept_ra_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");
>> }
>> if (rt)
>> dst_metric_set(&rt->dst, RTAX_HOPLIMIT,
>>
>
> Please see my comments against your previous patch.
I pasted you comments here so we don't need to discuss in two mails :)
>
> ra_msg->icmph.icmp6_hop_limit != 0 is checkd by outer "if".
Yes, thanks for your reminding :)
>
> You do not need to update cnf.hop_limit if it is already equal to
> hop limit received.
We need to update cnf.hop_limit if min_hop_limit <= icmp6_hop_limit. e.g.
current hop limit is 64, min hop limit is 1 and ra hop limit is 32, then we need
update current hop limit to 32.
>
> How about ignoring hop limit without message is configured value is
> larger than 255, BTW?
Although set accept_ra_min_hop_limit great than 255 is meaningless, there
is also no need to check it since icmp6_hop_limit will not larger than 255. so
+ if (in6_dev->cnf.accept_ra_min_hop_limit <= 255 &&
+ 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;
is duplicated check. How do you think?
>
>> if (rt)
>> dst_metric_set(&rt->dst, RTAX_HOPLIMIT,
>>
>
> This can be inside the inner "if".
OK, will move it.
Best Regards
Hangbin
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