ipv4: Create and use fib_compute_spec_dst() helper.

The specific destination is the host we direct unicast replies to.
Usually this is the original packet source address, but if we are
responding to a multicast or broadcast packet we have to use something
different.

Specifically we must use the source address we would use if we were to
send a packet to the unicast source of the original packet.

The routing cache precomputes this value, but we want to remove that
precomputation because it creates a hard dependency on the expensive
rpfilter source address validation which we'd like to make cheaper.

There are only three places where this matters:

1) ICMP replies.

2) pktinfo CMSG

3) IP options

Now there will be no real users of rt->rt_spec_dst and we can simply
remove it altogether.

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

1 files changed, 11 insertions, 11 deletions

diff --git a/net/ipv4/ip_options.c b/net/ipv4/ip_options.c
index 708b99494e23..766dfe56885a 100644
--- a/net/ipv4/ip_options.c
+++ b/net/ipv4/ip_options.c
@@ -27,6 +27,7 @@
 #include <net/icmp.h>
 #include <net/route.h>
 #include <net/cipso_ipv4.h>
+#include <net/ip_fib.h>
 
 /*
  * Write options to IP header, record destination address to
@@ -104,7 +105,7 @@ int ip_options_echo(struct ip_options *dopt, struct sk_buff *skb)
         sptr = skb_network_header(skb);
         dptr = dopt->__data;
 
-        daddr = skb_rtable(skb)->rt_spec_dst;
+        daddr = fib_compute_spec_dst(skb);
 
         if (sopt->rr) {
                 optlen  = sptr[sopt->rr+1];
@@ -250,15 +251,14 @@ void ip_options_fragment(struct sk_buff *skb)
 int ip_options_compile(struct net *net,
                        struct ip_options *opt, struct sk_buff *skb)
 {
-        int l;
-        unsigned char *iph;
-        unsigned char *optptr;
-        int optlen;
+        __be32 spec_dst = (__force __be32) 0;
         unsigned char *pp_ptr = NULL;
-        struct rtable *rt = NULL;
+        unsigned char *optptr;
+        unsigned char *iph;
+        int optlen, l;
 
         if (skb != NULL) {
-                rt = skb_rtable(skb);
+                spec_dst = fib_compute_spec_dst(skb);
                 optptr = (unsigned char *)&(ip_hdr(skb)[1]);
         } else
                 optptr = opt->__data;
@@ -330,8 +330,8 @@ int ip_options_compile(struct net *net,
                                         pp_ptr = optptr + 2;
                                         goto error;
                                 }
-                                if (rt) {
-                                        memcpy(&optptr[optptr[2]-1], &rt->rt_spec_dst, 4);
+                                if (skb) {
+                                        memcpy(&optptr[optptr[2]-1], &spec_dst, 4);
                                         opt->is_changed = 1;
                                 }
                                 optptr[2] += 4;
@@ -372,8 +372,8 @@ int ip_options_compile(struct net *net,
                                                 goto error;
                                         }
                                         opt->ts = optptr - iph;
-                                        if (rt)  {
-                                                memcpy(&optptr[optptr[2]-1], &rt->rt_spec_dst, 4);
+                                        if (skb)  {
+                                                memcpy(&optptr[optptr[2]-1], &spec_dst, 4);
                                                 timeptr = &optptr[optptr[2]+3];
                                         }
                                         opt->ts_needaddr = 1;