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Subject[PATCH 3.2 095/115] net/ipv6: add sysctl option accept_ra_min_hop_limit
3.2.80-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Hangbin Liu <liuhangbin@gmail.com>

[ 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>
[bwh: Backported to 3.2:
- Adjust filename, context
- Number DEVCONF enumerators explicitly to match upstream]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -1070,6 +1070,14 @@ 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.

--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -153,6 +153,7 @@ 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;
@@ -213,6 +214,8 @@ enum {
DEVCONF_DISABLE_IPV6,
DEVCONF_ACCEPT_DAD,
DEVCONF_FORCE_TLLAO,
+ DEVCONF_USE_OIF_ADDRS_ONLY = 37,
+ DEVCONF_ACCEPT_RA_MIN_HOP_LIMIT,
DEVCONF_MAX
};

--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -185,6 +185,7 @@ static struct ipv6_devconf ipv6_devconf
#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,
@@ -219,6 +220,7 @@ static struct ipv6_devconf ipv6_devconf_
#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,
@@ -3943,6 +3945,7 @@ static inline void ipv6_store_devconf(st
#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;
@@ -4544,6 +4547,13 @@ static struct addrconf_sysctl_table
.maxlen = sizeof(int),
.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,
},
{
.procname = "accept_ra_pinfo",
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -1276,18 +1276,16 @@ static void ndisc_router_discovery(struc
if (rt)
rt->rt6i_expires = 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_PRINTK2(KERN_WARNING "RA: Got route advertisement with lower hop_limit than current\n");
+ ND_PRINTK2(KERN_WARNING "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:
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