net/ipv6: add sysctl option accept_ra_min_hop_limit

Commit ec4bfdd8176a ("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>

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 1a5ab21bcca51bfade172d6752c6d426e648c384..00d26d919459422eb0cc0da039e152dd271c8832 100644 (file)
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -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.
 

diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 06ed637225b87fa341c33fcf8899d93f6f560b1c..cb9dcad72372150f2ad0d76c229d5f63b07f74ff 100644 (file)
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -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;

diff --git a/include/uapi/linux/ipv6.h b/include/uapi/linux/ipv6.h
index 641a146ead7d2a9072190dcdb34677960d3334af..80f3b74446a1a3e56704550138e816014537e60f 100644 (file)
--- a/include/uapi/linux/ipv6.h
+++ b/include/uapi/linux/ipv6.h
@@ -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
 };
 

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index eb0c6a3a8a002351fc7df2287ba757492f7645c3..53e3a9d756b0d804e873c80a820383b756a0624b 100644 (file)
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -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,

diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 0a05b35a90fc946dc0de3ae76e4a682ca4438932..6e184e02fd3c7ca13f7e9c914184d61fa82a6670 100644 (file)
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -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: