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, 8 insertions, 0 deletions

diff --git a/tests/py/inet/tcp.t.payload b/tests/py/inet/tcp.t.payload
index 09538aed..2390a24e 100644
--- a/tests/py/inet/tcp.t.payload
+++ b/tests/py/inet/tcp.t.payload
@@ -436,6 +436,14 @@ inet test-inet input
   [ bitwise reg 1 = (reg=1 & 0x00000003 ) ^ 0x00000000 ]
   [ cmp eq reg 1 0x00000003 ]
 
+# tcp flags & (fin | syn | rst | psh | ack | urg | ecn | cwr) == fin | syn | rst | psh | ack | urg | ecn | cwr
+inet test-inet input
+  [ meta load l4proto => reg 1 ]
+  [ cmp eq reg 1 0x00000006 ]
+  [ payload load 1b @ transport header + 13 => reg 1 ]
+  [ bitwise reg 1 = (reg=1 & 0x000000ff ) ^ 0x00000000 ]
+  [ cmp eq reg 1 0x000000ff ]
+
 # tcp window 22222
 inet test-inet input
   [ meta load l4proto => reg 1 ]