net: ipv6: Add sysctl for minimum prefix len acceptable in RIOs.

This commit adds a new sysctl accept_ra_rt_info_min_plen that
defines the minimum acceptable prefix length of Route Information
Options. The new sysctl is intended to be used together with
accept_ra_rt_info_max_plen to configure a range of acceptable
prefix lengths. It is useful to prevent misconfigurations from
unintentionally blackholing too much of the IPv6 address space
(e.g., home routers announcing RIOs for fc00::/7, which is
incorrect).

Signed-off-by: Joel Scherpelz <jscherpelz@google.com>
Acked-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

6 files changed, 26 insertions, 2 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index b57308e76b1d..eaee2c8d4c00 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -1461,11 +1461,20 @@ accept_ra_pinfo - BOOLEAN
         Functional default: enabled if accept_ra is enabled.
                             disabled if accept_ra is disabled.
 
+accept_ra_rt_info_min_plen - INTEGER
+        Minimum prefix length of Route Information in RA.
+
+        Route Information w/ prefix smaller than this variable shall
+        be ignored.
+
+        Functional default: 0 if accept_ra_rtr_pref is enabled.
+                            -1 if accept_ra_rtr_pref is disabled.
+
 accept_ra_rt_info_max_plen - INTEGER
         Maximum prefix length of Route Information in RA.
 
-        Route Information w/ prefix larger than or equal to this
-        variable shall be ignored.
+        Route Information w/ prefix larger than this variable shall
+        be ignored.
 
         Functional default: 0 if accept_ra_rtr_pref is enabled.
                             -1 if accept_ra_rtr_pref is disabled.
diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index f0d79bd054ca..e1b442996f81 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -37,6 +37,7 @@ struct ipv6_devconf {
         __s32           accept_ra_rtr_pref;
         __s32           rtr_probe_interval;
 #ifdef CONFIG_IPV6_ROUTE_INFO
+        __s32           accept_ra_rt_info_min_plen;
         __s32           accept_ra_rt_info_max_plen;
 #endif
 #endif
diff --git a/include/uapi/linux/ipv6.h b/include/uapi/linux/ipv6.h
index d8f6a1ac9af4..2ae59178189d 100644
--- a/include/uapi/linux/ipv6.h
+++ b/include/uapi/linux/ipv6.h
@@ -184,6 +184,7 @@ enum {
         DEVCONF_ENHANCED_DAD,
         DEVCONF_ADDR_GEN_MODE,
         DEVCONF_DISABLE_POLICY,
+        DEVCONF_ACCEPT_RA_RT_INFO_MIN_PLEN,
         DEVCONF_MAX
 };
 
diff --git a/include/uapi/linux/sysctl.h b/include/uapi/linux/sysctl.h
index d2b12152e358..e13d48058b8d 100644
--- a/include/uapi/linux/sysctl.h
+++ b/include/uapi/linux/sysctl.h
@@ -568,6 +568,7 @@ enum {
         NET_IPV6_PROXY_NDP=23,
         NET_IPV6_ACCEPT_SOURCE_ROUTE=25,
         NET_IPV6_ACCEPT_RA_FROM_LOCAL=26,
+        NET_IPV6_ACCEPT_RA_RT_INFO_MIN_PLEN=27,
         __NET_IPV6_MAX
 };
 
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 8c69768a5c46..dff5beb26a01 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -224,6 +224,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
         .accept_ra_rtr_pref     = 1,
         .rtr_probe_interval     = 60 * HZ,
 #ifdef CONFIG_IPV6_ROUTE_INFO
+        .accept_ra_rt_info_min_plen = 0,
         .accept_ra_rt_info_max_plen = 0,
 #endif
 #endif
@@ -277,6 +278,7 @@ static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
         .accept_ra_rtr_pref     = 1,
         .rtr_probe_interval     = 60 * HZ,
 #ifdef CONFIG_IPV6_ROUTE_INFO
+        .accept_ra_rt_info_min_plen = 0,
         .accept_ra_rt_info_max_plen = 0,
 #endif
 #endif
@@ -4979,6 +4981,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
         array[DEVCONF_RTR_PROBE_INTERVAL] =
                 jiffies_to_msecs(cnf->rtr_probe_interval);
 #ifdef CONFIG_IPV6_ROUTE_INFO
+        array[DEVCONF_ACCEPT_RA_RT_INFO_MIN_PLEN] = cnf->accept_ra_rt_info_min_plen;
         array[DEVCONF_ACCEPT_RA_RT_INFO_MAX_PLEN] = cnf->accept_ra_rt_info_max_plen;
 #endif
 #endif
@@ -6122,6 +6125,13 @@ static const struct ctl_table addrconf_sysctl[] = {
         },
 #ifdef CONFIG_IPV6_ROUTE_INFO
         {
+                .procname       = "accept_ra_rt_info_min_plen",
+                .data           = &ipv6_devconf.accept_ra_rt_info_min_plen,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = proc_dointvec,
+        },
+        {
                 .procname       = "accept_ra_rt_info_max_plen",
                 .data           = &ipv6_devconf.accept_ra_rt_info_max_plen,
                 .maxlen         = sizeof(int),
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 112ccbc0a8ac..b5812b3f7539 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -1418,6 +1418,8 @@ skip_linkparms:
                         if (ri->prefix_len == 0 &&
                             !in6_dev->cnf.accept_ra_defrtr)
                                 continue;
+                        if (ri->prefix_len < in6_dev->cnf.accept_ra_rt_info_min_plen)
+                                continue;
                         if (ri->prefix_len > in6_dev->cnf.accept_ra_rt_info_max_plen)
                                 continue;
                         rt6_route_rcv(skb->dev, (u8 *)p, (p->nd_opt_len) << 3,