parser_bison: Fix for ECN keyword in LHS of relational

Of all possible TCP flags, 'ecn' is special since it is recognized by
lex as a keyword (there is a a field in IPv4 and IPv6 headers with the
same name). Therefore it is listed in keyword_expr, but that was
sufficient for RHS only. The following statement reproduces the issue:

| tcp flags & (syn | ecn) == (syn | ecn)

The solution is to limit binop expressions to accept an RHS expression
on RHS ("real" LHS expressions don't make much sense there anyway),
which then allows keyword_expr to occur there. In order to maintain the
recursive behaviour if braces are present, allow primary_rhs_expr to
consist of a basic_rhs_expr enclosed in braces. This in turn requires
for braced RHS part in relational_expr to be dropped, otherwise bison
complains about shift/reduce conflict.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/tests/py/inet/tcp.t.json b/tests/py/inet/tcp.t.json
index 5744e594..babe5920 100644
--- a/tests/py/inet/tcp.t.json
+++ b/tests/py/inet/tcp.t.json
@@ -1101,6 +1101,29 @@
     }
 ]
 
+# tcp flags & (fin | syn | rst | psh | ack | urg | ecn | cwr) == fin | syn | rst | psh | ack | urg | ecn | cwr
+[
+    {
+        "match": {
+            "left": {
+                "&": [
+                    {
+                        "payload": {
+                            "field": "flags",
+                            "protocol": "tcp"
+                        }
+                    },
+                    {
+                        "|": [ "fin", { "|": [ "syn", { "|": [ "rst", { "|": [ "psh", { "|": [ "ack", { "|": [ "urg", { "|": [ "ecn", "cwr" ] } ] } ] } ] } ] } ] } ]
+                    }
+                ]
+            },
+            "op": "==",
+            "right": { "|": [ "fin", { "|": [ "syn", { "|": [ "rst", { "|": [ "psh", { "|": [ "ack", { "|": [ "urg", { "|": [ "ecn", "cwr" ] } ] } ] } ] } ] } ] } ] }
+        }
+    }
+]
+
 # tcp window 22222
 [
     {