ipv4: Fix bugs in fib_compute_spec_dst().

Based upon feedback from Julian Anastasov.

1) Use route flags to determine multicast/broadcast, not the
   packet flags.

2) Leave saddr unspecified in flow key.

3) Adjust how we invoke inet_select_addr().  Pass ip_hdr(skb)->saddr as
   second arg, and if it was zeronet use link scope.

4) Use loopback as input interface in flow key.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 21 insertions, 13 deletions

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 63b11ca54d95..1d13217e01ff 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -185,28 +185,36 @@ __be32 fib_compute_spec_dst(struct sk_buff *skb)
         struct net_device *dev = skb->dev;
         struct in_device *in_dev;
         struct fib_result res;
+        struct rtable *rt;
         struct flowi4 fl4;
         struct net *net;
+        int scope;
 
-        if (skb->pkt_type != PACKET_BROADCAST &&
-            skb->pkt_type != PACKET_MULTICAST)
+        rt = skb_rtable(skb);
+        if (!(rt->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST)))
                 return ip_hdr(skb)->daddr;
 
         in_dev = __in_dev_get_rcu(dev);
         BUG_ON(!in_dev);
-        fl4.flowi4_oif = 0;
-        fl4.flowi4_iif = 0;
-        fl4.daddr = ip_hdr(skb)->saddr;
-        fl4.saddr = ip_hdr(skb)->daddr;
-        fl4.flowi4_tos = RT_TOS(ip_hdr(skb)->tos);
-        fl4.flowi4_scope = RT_SCOPE_UNIVERSE;
-        fl4.flowi4_mark = IN_DEV_SRC_VMARK(in_dev) ? skb->mark : 0;
 
         net = dev_net(dev);
-        if (!fib_lookup(net, &fl4, &res))
-                return FIB_RES_PREFSRC(net, res);
-        else
-                return inet_select_addr(dev, 0, RT_SCOPE_UNIVERSE);
+
+        scope = RT_SCOPE_UNIVERSE;
+        if (!ipv4_is_zeronet(ip_hdr(skb)->saddr)) {
+                fl4.flowi4_oif = 0;
+                fl4.flowi4_iif = net->loopback_dev->ifindex;
+                fl4.daddr = ip_hdr(skb)->saddr;
+                fl4.saddr = 0;
+                fl4.flowi4_tos = RT_TOS(ip_hdr(skb)->tos);
+                fl4.flowi4_scope = scope;
+                fl4.flowi4_mark = IN_DEV_SRC_VMARK(in_dev) ? skb->mark : 0;
+                if (!fib_lookup(net, &fl4, &res))
+                        return FIB_RES_PREFSRC(net, res);
+        } else {
+                scope = RT_SCOPE_LINK;
+        }
+
+        return inet_select_addr(dev, ip_hdr(skb)->saddr, scope);
 }
 
 /* Given (packet source, input interface) and optional (dst, oif, tos):