[nft PATCH 1/3] evaluate: check for NULL datatype in rhs in lookup expr

[Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>]

If we are evaluating an EXPR_SET_REF, check if right->dtype is not NULL.
We can hit SEGFAULT if for whatever reason the referenced object does not
exists.

Using this testfile (note the invalid set syntax):

% cat test.nft
flush ruleset
add table t
add chain t c
add set t s {type ipv4_addr\;}
add rule t c ip saddr @s

Without this patch:

% nft -f test.nft
Segmentation fault

With this patch:

% nft -f test.nft
t.nft:4:28-28: Error: syntax error, unexpected junk, expecting newline or semicolon
add set t s {type ipv4_addr\;}
                           ^
t.nft:4:13-29: Error: set definition does not specify key data type
add set t s {type ipv4_addr\;}
            ^^^^^^^^^^^^^^^^^
t.nft:5:23-24: Error: the referenced object does not exists
add rule t c ip saddr @s
             ~~~~~~~~ ^^

Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>
---
 src/evaluate.c |   35 ++++++++++++++++++++++++++---------
 1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/src/evaluate.c b/src/evaluate.c
index 7444d09..6840790 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -1210,16 +1210,33 @@ static int expr_evaluate_relational(struct eval_ctx *ctx, struct expr **expr)
 
 	switch (rel->op) {
 	case OP_LOOKUP:
-		/* A literal set expression implicitly declares the set */
-		if (right->ops->type == EXPR_SET)
+		switch (right->ops->type) {
+		case EXPR_SET:
+			/* A literal set expression implicitly declares
+			 * the set
+			 */
 			right = rel->right =
-				implicit_set_declaration(ctx, left->dtype, left->len, right);
-		else if (!datatype_equal(left->dtype, right->dtype))
-			return expr_binary_error(ctx->msgs, right, left,
-						 "datatype mismatch, expected %s, "
-						 "set has type %s",
-						 left->dtype->desc,
-						 right->dtype->desc);
+				implicit_set_declaration(ctx, left->dtype,
+							 left->len, right);
+			break;
+		case EXPR_SET_REF:
+			if (right->dtype == NULL)
+				return expr_binary_error(ctx->msgs, right,
+							 left, "the referenced"
+							 " object does not "
+							 "exists");
+			if (!datatype_equal(left->dtype, right->dtype))
+				return expr_binary_error(ctx->msgs, right,
+							 left, "datatype "
+							 "mismatch, expected "
+							 "%s, set has type %s",
+							 left->dtype->desc,
+							 right->dtype->desc);
+			break;
+		default:
+			BUG("unhandled right expression type %u\n",
+			    right->ops->type);
+		}
 
 		/* Data for range lookups needs to be in big endian order */
 		if (right->set->flags & SET_F_INTERVAL &&