evaluate: don't evaluate payloads twice.

Payload munging means that evaluation of payload expressions may not be
idempotent.  Add a flag to prevent them from being evaluated more than
once.

Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
Signed-off-by: Florian Westphal <fw@strlen.de>

2 files changed, 6 insertions, 0 deletions

diff --git a/include/expression.h b/include/expression.h
index 62fbbbb5..87c39e5d 100644
--- a/include/expression.h
+++ b/include/expression.h
@@ -300,6 +300,7 @@ struct expr {
 			enum proto_bases		base;
 			unsigned int			offset;
 			bool				is_raw;
+			bool				evaluated;
 		} payload;
 		struct {
 			/* EXPR_EXTHDR */
diff --git a/src/evaluate.c b/src/evaluate.c
index e2eff235..a169e41b 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -736,6 +736,9 @@ static int expr_evaluate_payload(struct eval_ctx *ctx, struct expr **exprp)
 {
 	struct expr *expr = *exprp;
 
+	if (expr->payload.evaluated)
+		return 0;
+
 	if (__expr_evaluate_payload(ctx, expr) < 0)
 		return -1;
 
@@ -745,6 +748,8 @@ static int expr_evaluate_payload(struct eval_ctx *ctx, struct expr **exprp)
 	if (payload_needs_adjustment(expr))
 		expr_evaluate_bits(ctx, exprp);
 
+	expr->payload.evaluated = true;
+
 	return 0;
 }