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).

[backport of net-next bbea124bc9]
Bug: 33333670
Test: net_test passes

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

include/uapi/linux/ipv6.h

@@ -175,6 +175,16 @@ enum {
 	DEVCONF_USE_OIF_ADDRS_ONLY,
 	DEVCONF_ACCEPT_RA_MIN_HOP_LIMIT,
 	DEVCONF_IGNORE_ROUTES_WITH_LINKDOWN,
+	DEVCONF_DROP_UNICAST_IN_L2_MULTICAST,
+	DEVCONF_DROP_UNSOLICITED_NA,
+	DEVCONF_KEEP_ADDR_ON_DOWN,
+	DEVCONF_RTR_SOLICIT_MAX_INTERVAL,
+	DEVCONF_SEG6_ENABLED,
+	DEVCONF_SEG6_REQUIRE_HMAC,
+	DEVCONF_ENHANCED_DAD,
+	DEVCONF_ADDR_GEN_MODE,
+	DEVCONF_DISABLE_POLICY,
+	DEVCONF_ACCEPT_RA_RT_INFO_MIN_PLEN,
 	DEVCONF_MAX
 };
 

include/uapi/linux/sysctl.h

@@ -570,6 +570,7 @@ 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
 };