ipv4 unicast nlri checking

- addresses #210 for ipv4

bgp/src/error.rs

@@ -5,6 +5,7 @@
 use std::{fmt::Display, net::IpAddr};
 
 use num_enum::TryFromPrimitiveError;
+use rdb::Prefix4;
 
 #[derive(thiserror::Error, Debug)]
 pub enum Error {
@@ -168,6 +169,15 @@ pub enum Error {
 
     #[error("Hold time too small")]
     HoldTimeTooSmall,
+
+    #[error("Invalid NLRI prefix")]
+    InvalidNlriPrefix(Prefix4),
+
+    #[error("Nexthop cannot equal prefix")]
+    NexthopSelf(IpAddr),
+
+    #[error("Nexthop missing")]
+    MissingNexthop,
 }
 
 #[derive(Debug)]

bgp/src/session.rs

@@ -1634,6 +1634,8 @@ impl<Cnx: BgpConnection + 'static> SessionRunner<Cnx> {
     /// Perform a set of checks on an update to see if we can accept it.
     fn check_update(&self, update: &UpdateMessage) -> Result<(), Error> {
         self.check_for_self_in_path(update)?;
+        self.check_v4_prefixes(update)?;
+        self.check_nexthop_self(update)?;
         let info = lock!(self.session);
         if info.enforce_first_as {
             if let Some(peer_as) = info.remote_asn {
@@ -1675,6 +1677,41 @@ impl<Cnx: BgpConnection + 'static> SessionRunner<Cnx> {
         Ok(())
     }
 
+    //TODO similar check needed for v6 once we get full v6 support
+    fn check_v4_prefixes(&self, update: &UpdateMessage) -> Result<(), Error> {
+        for prefix in &update.nlri {
+            if prefix.length == 0 {
+                continue;
+            }
+            let first = prefix.value[0];
+            // check 127.0.0.0/8, 224.0.0.0/4, 240.0.0.0/4
+            if (first == 127) || (first & 0xf0 == 224) || (first & 0xf0 == 240)
+            {
+                return Err(Error::InvalidNlriPrefix(prefix.as_prefix4()));
+            }
+        }
+        Ok(())
+    }
+
+    fn check_nexthop_self(&self, update: &UpdateMessage) -> Result<(), Error> {
+        // nothing to check when no prefixes presnt, and nexthop not required
+        // for pure withdraw
+        if update.nlri.is_empty() {
+            return Ok(());
+        }
+        let nexthop = match update.nexthop4() {
+            Some(nh) => nh,
+            None => return Err(Error::MissingNexthop),
+        };
+        for prefix in &update.nlri {
+            let prefix = prefix.as_prefix4();
+            if prefix.length == 32 && prefix.value == nexthop {
+                return Err(Error::NexthopSelf(prefix.value.into()));
+            }
+        }
+        Ok(())
+    }
+
     fn enforce_first_as(
         &self,
         update: &UpdateMessage,