ipv4: Loosen source address check on IPv4 output

ip_route_output() contains a check to make sure that no flows with
non-local source IP addresses are routed. This obviously makes using
such addresses impossible.

This patch introduces a flowi flag which makes omitting this check
possible. The new flag provides a way of handling transparent and
non-transparent connections differently.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: KOVACS Krisztian <hidden@sch.bme.hu>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 15 insertions, 7 deletions

diff --git a/include/net/flow.h b/include/net/flow.h
index 228b2477ceec..b45a5e4fcadd 100644
--- a/include/net/flow.h
+++ b/include/net/flow.h
@@ -47,6 +47,8 @@ struct flowi {
 #define fl4_scope       nl_u.ip4_u.scope
 
         __u8    proto;
+        __u8    flags;
+#define FLOWI_FLAG_ANYSRC 0x01
         union {
                 struct {
                         __be16  sport;
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index f62187bb6d08..a6d7c584f53b 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2361,11 +2361,6 @@ static int ip_route_output_slow(struct net *net, struct rtable **rp,
                     ipv4_is_zeronet(oldflp->fl4_src))
                         goto out;
 
-                /* It is equivalent to inet_addr_type(saddr) == RTN_LOCAL */
-                dev_out = ip_dev_find(net, oldflp->fl4_src);
-                if (dev_out == NULL)
-                        goto out;
-
                 /* I removed check for oif == dev_out->oif here.
                    It was wrong for two reasons:
                    1. ip_dev_find(net, saddr) can return wrong iface, if saddr
@@ -2377,6 +2372,11 @@ static int ip_route_output_slow(struct net *net, struct rtable **rp,
                 if (oldflp->oif == 0
                     && (ipv4_is_multicast(oldflp->fl4_dst) ||
                         oldflp->fl4_dst == htonl(0xFFFFFFFF))) {
+                        /* It is equivalent to inet_addr_type(saddr) == RTN_LOCAL */
+                        dev_out = ip_dev_find(net, oldflp->fl4_src);
+                        if (dev_out == NULL)
+                                goto out;
+
                         /* Special hack: user can direct multicasts
                            and limited broadcast via necessary interface
                            without fiddling with IP_MULTICAST_IF or IP_PKTINFO.
@@ -2395,9 +2395,15 @@ static int ip_route_output_slow(struct net *net, struct rtable **rp,
                         fl.oif = dev_out->ifindex;
                         goto make_route;
                 }
-                if (dev_out)
+
+                if (!(oldflp->flags & FLOWI_FLAG_ANYSRC)) {
+                        /* It is equivalent to inet_addr_type(saddr) == RTN_LOCAL */
+                        dev_out = ip_dev_find(net, oldflp->fl4_src);
+                        if (dev_out == NULL)
+                                goto out;
                         dev_put(dev_out);
-                dev_out = NULL;
+                        dev_out = NULL;
+                }
         }