ipv4: Cap ADVMSS metric in the FIB rather than the routing cache.

It makes no sense to execute this limit test every time we create a
routing cache entry.

We can't simply error out on these things since we've silently
accepted and truncated them forever.

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

1 files changed, 6 insertions, 1 deletions

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index e5b7182fa099..415f8230fc88 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -779,9 +779,14 @@ struct fib_info *fib_create_info(struct fib_config *cfg)
                         int type = nla_type(nla);
 
                         if (type) {
+                                u32 val;
+
                                 if (type > RTAX_MAX)
                                         goto err_inval;
-                                fi->fib_metrics[type - 1] = nla_get_u32(nla);
+                                val = nla_get_u32(nla);
+                                if (type == RTAX_ADVMSS && val > 65535 - 40)
+                                        val = 65535 - 40;
+                                fi->fib_metrics[type - 1] = val;
                         }
                 }
         }