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>

5 files changed, 27 insertions, 15 deletions

diff --git a/include/linux/snmp.h b/include/linux/snmp.h
index 52797714ade7..ebb0c80ffd6e 100644
--- a/include/linux/snmp.h
+++ b/include/linux/snmp.h
@@ -229,6 +229,7 @@ enum
         LINUX_MIB_TCPBACKLOGDROP,
         LINUX_MIB_TCPMINTTLDROP, /* RFC 5082 */
         LINUX_MIB_TCPDEFERACCEPTDROP,
+        LINUX_MIB_IPRPFILTER, /* IP Reverse Path Filter (rp_filter) */
         __LINUX_MIB_MAX
 };
 
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)
diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
index d930dc5e4d85..d52c9da644cf 100644
--- a/net/ipv4/ip_input.c
+++ b/net/ipv4/ip_input.c
@@ -340,6 +340,9 @@ static int ip_rcv_finish(struct sk_buff *skb)
                         else if (err == -ENETUNREACH)
                                 IP_INC_STATS_BH(dev_net(skb->dev),
                                                 IPSTATS_MIB_INNOROUTES);
+                        else if (err == -EXDEV)
+                                NET_INC_STATS_BH(dev_net(skb->dev),
+                                                 LINUX_MIB_IPRPFILTER);
                         goto drop;
                 }
         }
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 3dc9914c1dce..e320ca6b3ef3 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -252,6 +252,7 @@ static const struct snmp_mib snmp4_net_list[] = {
         SNMP_MIB_ITEM("TCPBacklogDrop", LINUX_MIB_TCPBACKLOGDROP),
         SNMP_MIB_ITEM("TCPMinTTLDrop", LINUX_MIB_TCPMINTTLDROP),
         SNMP_MIB_ITEM("TCPDeferAcceptDrop", LINUX_MIB_TCPDEFERACCEPTDROP),
+        SNMP_MIB_ITEM("IPReversePathFilter", LINUX_MIB_IPRPFILTER),
         SNMP_MIB_SENTINEL
 };
 
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 8495bceec764..d377b45005fc 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1851,6 +1851,7 @@ static int ip_route_input_mc(struct sk_buff *skb, __be32 daddr, __be32 saddr,
         __be32 spec_dst;
         struct in_device *in_dev = in_dev_get(dev);
         u32 itag = 0;
+        int err;
 
         /* Primary sanity checks. */
 
@@ -1865,10 +1866,12 @@ static int ip_route_input_mc(struct sk_buff *skb, __be32 daddr, __be32 saddr,
                 if (!ipv4_is_local_multicast(daddr))
                         goto e_inval;
                 spec_dst = inet_select_addr(dev, 0, RT_SCOPE_LINK);
-        } else if (fib_validate_source(saddr, 0, tos, 0,
-                                        dev, &spec_dst, &itag, 0) < 0)
-                goto e_inval;
-
+        } else {
+                err = fib_validate_source(saddr, 0, tos, 0, dev, &spec_dst,
+                                          &itag, 0);
+                if (err < 0)
+                        goto e_err;
+        }
         rth = dst_alloc(&ipv4_dst_ops);
         if (!rth)
                 goto e_nobufs;
@@ -1920,8 +1923,10 @@ e_nobufs:
         return -ENOBUFS;
 
 e_inval:
+        err = -EINVAL;
+e_err:
         in_dev_put(in_dev);
-        return -EINVAL;
+        return err;
 }
 
 
@@ -1985,7 +1990,6 @@ static int __mkroute_input(struct sk_buff *skb,
                 ip_handle_martian_source(in_dev->dev, in_dev, skb, daddr,
                                          saddr);
 
-                err = -EINVAL;
                 goto cleanup;
         }
 
@@ -2157,13 +2161,12 @@ static int ip_route_input_slow(struct sk_buff *skb, __be32 daddr, __be32 saddr,
                 goto brd_input;
 
         if (res.type == RTN_LOCAL) {
-                int result;
-                result = fib_validate_source(saddr, daddr, tos,
+                err = fib_validate_source(saddr, daddr, tos,
                                              net->loopback_dev->ifindex,
                                              dev, &spec_dst, &itag, skb->mark);
-                if (result < 0)
-                        goto martian_source;
-                if (result)
+                if (err < 0)
+                        goto martian_source_keep_err;
+                if (err)
                         flags |= RTCF_DIRECTSRC;
                 spec_dst = daddr;
                 goto local_input;
@@ -2191,7 +2194,7 @@ brd_input:
                 err = fib_validate_source(saddr, 0, tos, 0, dev, &spec_dst,
                                           &itag, skb->mark);
                 if (err < 0)
-                        goto martian_source;
+                        goto martian_source_keep_err;
                 if (err)
                         flags |= RTCF_DIRECTSRC;
         }
@@ -2272,8 +2275,10 @@ e_nobufs:
         goto done;
 
 martian_source:
+        err = -EINVAL;
+martian_source_keep_err:
         ip_handle_martian_source(dev, in_dev, skb, daddr, saddr);
-        goto e_inval;
+        goto done;
 }
 
 int ip_route_input_common(struct sk_buff *skb, __be32 daddr, __be32 saddr,