ipv4: Restore accept_local behaviour in fib_validate_source()

Commit 7a9bc9b81a5b ("ipv4: Elide fib_validate_source() completely when possible.")
introduced a short-circuit to avoid calling fib_validate_source when not
needed. That change took rp_filter into account, but not accept_local.
This resulted in a change of behaviour: with rp_filter and accept_local
off, incoming packets with a local address in the source field should be
dropped.

Here is how to reproduce the change pre/post 7a9bc9b81a5b commit:
-configure the same IPv4 address on hosts A and B.
-try to send an ARP request from B to A.
-The ARP request will be dropped before that commit, but accepted and answered
after that commit.

This adds a check for ACCEPT_LOCAL, to maintain full
fib validation in case it is 0. We also leave __fib_validate_source() earlier
when possible, based on the same check as fib_validate_source(), once the
accept_local stuff is verified.

Cc: Gregory Detal <gregory.detal@uclouvain.be>
Cc: Christoph Paasch <christoph.paasch@uclouvain.be>
Cc: Hannes Frederic Sowa <hannes@redhat.com>
Cc: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Sébastien Barré <sebastien.barre@uclouvain.be>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 6 deletions

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 255aa9946fe7..23104a3f2924 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -243,7 +243,7 @@ static int __fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
                                  u8 tos, int oif, struct net_device *dev,
                                  int rpf, struct in_device *idev, u32 *itag)
 {
-        int ret, no_addr, accept_local;
+        int ret, no_addr;
         struct fib_result res;
         struct flowi4 fl4;
         struct net *net;
@@ -258,16 +258,17 @@ static int __fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
 
         no_addr = idev->ifa_list == NULL;
 
-        accept_local = IN_DEV_ACCEPT_LOCAL(idev);
         fl4.flowi4_mark = IN_DEV_SRC_VMARK(idev) ? skb->mark : 0;
 
         net = dev_net(dev);
         if (fib_lookup(net, &fl4, &res))
                 goto last_resort;
-        if (res.type != RTN_UNICAST) {
-                if (res.type != RTN_LOCAL || !accept_local)
-                        goto e_inval;
-        }
+        if (res.type != RTN_UNICAST &&
+            (res.type != RTN_LOCAL || !IN_DEV_ACCEPT_LOCAL(idev)))
+                goto e_inval;
+        if (!rpf && !fib_num_tclassid_users(dev_net(dev)) &&
+            (dev->ifindex != oif || !IN_DEV_TX_REDIRECTS(idev)))
+                goto last_resort;
         fib_combine_itag(itag, &res);
         dev_match = false;
 
@@ -321,6 +322,7 @@ int fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
         int r = secpath_exists(skb) ? 0 : IN_DEV_RPFILTER(idev);
 
         if (!r && !fib_num_tclassid_users(dev_net(dev)) &&
+            IN_DEV_ACCEPT_LOCAL(idev) &&
             (dev->ifindex != oif || !IN_DEV_TX_REDIRECTS(idev))) {
                 *itag = 0;
                 return 0;