ipv4: Allow configuring subnets as local addresses

This patch allows a host to be configured to respond to any address in
a specified range as if it were local, without actually needing to
configure the address on an interface.  This is done through routing
table configuration.  For instance, to configure a host to respond
to any address in 10.1/16 received on eth0 as a local address we can do:

ip rule add from all iif eth0 lookup 200
ip route add local 10.1/16 dev lo proto kernel scope host src 127.0.0.1 table 200

This host is now reachable by any 10.1/16 address (route lookup on
input for packets received on eth0 can find the route).  On output, the
rule will not be matched so that this host can still send packets to
10.1/16 (not sent on loopback).  Presumably, external routing can be
configured to make sense out of this.

To make this work, we needed to modify the logic in finding the
interface which is assigned a given source address for output
(dev_ip_find).  We perform a normal fib_lookup instead of just a
lookup on the local table, and in the lookup we ignore the input
interface for matching.

This patch is useful to implement IP-anycast for subnets of virtual
addresses.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/flow.h b/include/net/flow.h
index bb08692a20b08841ead94acce78c9ead82293d94..0ac3fb5e0973460f3046cdf1f00a0e1114a13dff 100644 (file)
--- a/include/net/flow.h
+++ b/include/net/flow.h
@@ -49,6 +49,7 @@ struct flowi {
        __u8    proto;
        __u8    flags;
 #define FLOWI_FLAG_ANYSRC 0x01
+#define FLOWI_FLAG_MATCH_ANY_IIF 0x02
        union {
                struct {
                        __be16  sport;

diff --git a/net/core/fib_rules.c b/net/core/fib_rules.c
index d0787284cb07ed3a2cc03e738b2509666c2d7f1a..332c2e31d048265841f2c2e7fc5147eab28d83d7 100644 (file)
--- a/net/core/fib_rules.c
+++ b/net/core/fib_rules.c
@@ -182,7 +182,8 @@ static int fib_rule_match(struct fib_rule *rule, struct fib_rules_ops *ops,
 {
        int ret = 0;
 
-       if (rule->iifindex && (rule->iifindex != fl->iif))
+       if (rule->iifindex && (rule->iifindex != fl->iif) &&
+           !(fl->flags & FLOWI_FLAG_MATCH_ANY_IIF))
                goto out;
 
        if (rule->oifindex && (rule->oifindex != fl->oif))

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 7d02a9f999fabcebeb61800816d722e6f6c054ff..981f3c59b33412b8674b1974ca1b4877cde97511 100644 (file)
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -153,17 +153,16 @@ static void fib_flush(struct net *net)
 
 struct net_device * ip_dev_find(struct net *net, __be32 addr)
 {
-       struct flowi fl = { .nl_u = { .ip4_u = { .daddr = addr } } };
+       struct flowi fl = { .nl_u = { .ip4_u = { .daddr = addr } },
+                           .flags = FLOWI_FLAG_MATCH_ANY_IIF };
        struct fib_result res;
        struct net_device *dev = NULL;
-       struct fib_table *local_table;
 
 #ifdef CONFIG_IP_MULTIPLE_TABLES
        res.r = NULL;
 #endif
 
-       local_table = fib_get_table(net, RT_TABLE_LOCAL);
-       if (!local_table || fib_table_lookup(local_table, &fl, &res))
+       if (fib_lookup(net, &fl, &res))
                return NULL;
        if (res.type != RTN_LOCAL)
                goto out;