[PATCH nft] evaluate: do not remove anonymous set with protocol flags and single element

[Pablo Neira Ayuso <pablo@netfilter.org>]

Set lookups with flags search for an exact match, however:

	tcp flags { syn }

gets transformed into:

	tcp flags syn

which is matching on the syn flag only (non-exact match).

This optimization is safe for ct state though, because only one bit is
ever set on in the ct state bitmask.

Since protocol flags allow for combining flags, skip this optimization
to retain exact match semantics.

Another possible solution is to turn OP_IMPLICIT into OP_EQ for exact
flag match to re-introduce this optimization to deal with this corner
case.

Fixes: fee6bda06403 ("evaluate: remove anon sets with exactly one element")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 src/evaluate.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/evaluate.c b/src/evaluate.c
index 1ae2ef0de10c..39b0077ce99e 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -1817,7 +1817,12 @@ static int expr_evaluate_set(struct eval_ctx *ctx, struct expr **expr)
 			set->set_flags |= NFT_SET_CONCAT;
 	} else if (set->size == 1) {
 		i = list_first_entry(&set->expressions, struct expr, list);
-		if (i->etype == EXPR_SET_ELEM && list_empty(&i->stmt_list)) {
+		if (i->etype == EXPR_SET_ELEM &&
+		    (!i->dtype->basetype ||
+		     i->dtype->basetype->type != TYPE_BITMASK ||
+		     i->dtype->type == TYPE_CT_STATE) &&
+		    list_empty(&i->stmt_list)) {
+
 			switch (i->key->etype) {
 			case EXPR_PREFIX:
 			case EXPR_RANGE:
-- 
2.30.2