[PATCH nft] evaluate: don't eval unary arguments.

[Jeremy Sowden <jeremy@azazel.net>]

When a unary expression is inserted to implement a byte-order
conversion, the expression being converted has already been evaluated
and so expr_evaluate_unary doesn't need to do so.  For most types of
expression, the double evaluation doesn't matter since evaluation is
idempotent.  However, in the case of payload expressions which are
munged during evaluation, it can cause unexpected errors:

  # nft add table ip t
  # nft add chain ip t c '{ type filter hook input priority filter; }'
  # nft add rule ip t c ip dscp set 'ip dscp | 0x10'
  Error: Value 252 exceeds valid range 0-63
  add rule ip t c ip dscp set ip dscp | 0x10
                              ^^^^^^^

Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
---
 src/evaluate.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/src/evaluate.c b/src/evaluate.c
index e7881543d2de..9d5fdaf0ef3e 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -997,13 +997,9 @@ static int expr_evaluate_range(struct eval_ctx *ctx, struct expr **expr)
  */
 static int expr_evaluate_unary(struct eval_ctx *ctx, struct expr **expr)
 {
-	struct expr *unary = *expr, *arg;
+	struct expr *unary = *expr, *arg = unary->arg;
 	enum byteorder byteorder;
 
-	if (expr_evaluate(ctx, &unary->arg) < 0)
-		return -1;
-	arg = unary->arg;
-
 	assert(!expr_is_constant(arg));
 	assert(expr_basetype(arg)->type == TYPE_INTEGER);
 	assert(arg->etype != EXPR_UNARY);
-- 
2.24.1