net/ipv6: add sysctl option accept_ra_min_hop_limit

[ 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>

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 3b979c6ba84b75679529f008e238165269b59a06..0df5824fee3b8a966b60af12bd02bc8eb1589b90 100644 (file)
--- 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.
 

diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 00ef00d0f3157b17bdbf37fe4472428d83f514ca..2729d09e9c1164f56de1ab5c6791108cc0b2a03a 100644 (file)
--- 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
 };
 

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 006867df01787571fce8d86066751dc6b00578d6..79eceab4637a2b67ac955609bd6adc367845a9fd 100644 (file)
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -185,6 +185,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
 #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_dflt __read_mostly = {
 #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(struct ipv6_devconf *cnf,
 #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;
@@ -4545,6 +4548,13 @@ 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,

diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 39836dafa931acdb27ad7bcbb7b3e1a6dedcc7ff..e5b0f9e0deaac84fd86df79dd614475dc3312b0d 100644 (file)
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -1276,18 +1276,16 @@ static void ndisc_router_discovery(struct sk_buff *skb)
        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: