smb: do not rely on one valid NBSS byte for probing

Need to have the SMB header so as to validate

rust/src/smb/nbss_records.rs

@@ -44,6 +44,9 @@ impl<'a> NbssRecord<'a> {
         };
         valid
     }
+    pub fn needs_more(&self) -> bool {
+        return self.is_valid() && self.length >= 4 && self.data.len() < 4;
+    }
     pub fn is_smb(&self) -> bool {
         let valid = self.is_valid();
         let smb = if self.data.len() >= 4 &&

rust/src/smb/smb.rs

@@ -1977,9 +1977,8 @@ pub extern "C" fn rs_smb_probe_tcp(direction: u8,
             if hdr.is_smb() {
                 SCLogDebug!("smb found");
                 return 1;
-            } else if hdr.is_valid() {
-                SCLogDebug!("nbss found, assume smb");
-                return 1;
+            } else if hdr.needs_more(){
+                return 0;
             }
         },
         _ => { },