src: detach set, list and concatenation expression layout

These three expressions use the same layout, but they have a different
purpose. Several fields are specific of a given expression:

- set_flags is only required by set expressions.
- field_len and field_count are only used by concatenation expressions.

Add accessors to validate the expression type before accessing the union
fields:

 #define expr_set(__expr)       (assert((__expr)->etype == EXPR_SET), &(__expr)->expr_set)
 #define expr_concat(__expr)    (assert((__expr)->etype == EXPR_CONCAT), &(__expr)->expr_concat)
 #define expr_list(__expr)      (assert((__expr)->etype == EXPR_LIST), &(__expr)->expr_list)

This should help catch subtle bugs due to type confusion.

assert() could be later enabled only in debugging builds to run tests,
keep it by now.

compound_expr_*() still works and it needs the same initial layout for
all of these expressions:

      struct list_head        expressions;
      unsigned int            size;

This is implicitly reducing the size of one of the largest structs
in the union area of struct expr, still EXPR_SET_ELEM remains the
largest so no gain is achieved in this iteration.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/src/parser_json.c b/src/parser_json.c
index 08657f28..bd865de5 100644
--- a/src/parser_json.c
+++ b/src/parser_json.c
@@ -1286,10 +1286,11 @@ static struct expr *json_parse_binop_expr(struct json_ctx *ctx,
 
 static struct expr *json_check_concat_expr(struct json_ctx *ctx, struct expr *e)
 {
-	if (e->size >= 2)
+	if (expr_concat(e)->size >= 2)
 		return e;
 
-	json_error(ctx, "Concatenation with %d elements is illegal", e->size);
+	json_error(ctx, "Concatenation with %d elements is illegal",
+		   expr_concat(e)->size);
 	expr_free(e);
 	return NULL;
 }