ipv4: add LINUX_MIB_IPRPFILTER snmp counter

Christoph Lameter mentioned that packets could be dropped in input path
because of rp_filter settings, without any SNMP counter being
incremented. System administrator can have a hard time to track the
problem.

This patch introduces a new counter, LINUX_MIB_IPRPFILTER, incremented
each time we drop a packet because Reverse Path Filter triggers.

(We receive an IPv4 datagram on a given interface, and find the route to
send an answer would use another interface)

netstat -s | grep IPReversePathFilter
    IPReversePathFilter: 21714

Reported-by: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 2 deletions

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 4f0ed458c883..e830f7a123bd 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -284,7 +284,7 @@ int fib_validate_source(__be32 src, __be32 dst, u8 tos, int oif,
         if (no_addr)
                 goto last_resort;
         if (rpf == 1)
-                goto e_inval;
+                goto e_rpf;
         fl.oif = dev->ifindex;
 
         ret = 0;
@@ -299,7 +299,7 @@ int fib_validate_source(__be32 src, __be32 dst, u8 tos, int oif,
 
 last_resort:
         if (rpf)
-                goto e_inval;
+                goto e_rpf;
         *spec_dst = inet_select_addr(dev, 0, RT_SCOPE_UNIVERSE);
         *itag = 0;
         return 0;
@@ -308,6 +308,8 @@ e_inval_res:
         fib_res_put(&res);
 e_inval:
         return -EINVAL;
+e_rpf:
+        return -EXDEV;
 }
 
 static inline __be32 sk_extract_addr(struct sockaddr *addr)