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net/ipv6: add sysctl option accept_ra_min_hop_limit

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Commit 6fd99094de ("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>
This commit is contained in:
Hangbin Liu 2015-07-30 14:28:42 +08:00 committed by David S. Miller
parent 2f51a9b8ad
commit 8013d1d7ea
5 changed files with 27 additions and 9 deletions
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8
Documentation/networking/ip-sysctl.txt
View File

@ -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.

1
include/linux/ipv6.h
View File

@ -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;

1
include/uapi/linux/ipv6.h
View File

@ -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
};

10
net/ipv6/addrconf.c
View File

@ -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;
@ -5484,6 +5487,13 @@ 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,
},
{
.procname = "accept_ra_pinfo",
.data = &ipv6_devconf.accept_ra_pinfo,

16
net/ipv6/ndisc.c
View File

@ -1225,18 +1225,16 @@ 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 < 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 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,
ra_msg->icmph.icmp6_hop_limit);
}
skip_defrtr: