json: fix error propagation when parsing binop lhs/rhs

commit 1b6470ab1c4eff46986e65db1b69278f13c26666 upstream.

Malformed input returns NULL when decoding left/right side of binop.
This causes a NULL dereference in expr_evaluate_binop; left/right must
point to a valid expression.

Fix this in the parser, else would have to sprinkle NULL checks all over
the evaluation code.

After fix, loading the bogon yields:
internal:0:0-0: Error: Malformed object (too many properties): '{}'.
internal:0:0-0: Error: could not decode binop rhs, '<<'.
internal:0:0-0: Error: Invalid mangle statement value
internal:0:0-0: Error: Parsing expr array at index 1 failed.
internal:0:0-0: Error: Parsing command array at index 3 failed.

Fixes: 0ac39384fd9e ("json: Accept more than two operands in binary expressions")
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/parser_json.c b/src/parser_json.c
index e8fed0d2..c7649ccf 100644
--- a/src/parser_json.c
+++ b/src/parser_json.c
@@ -1138,11 +1138,25 @@ static struct expr *json_parse_binop_expr(struct json_ctx *ctx,
 
 	if (json_array_size(root) > 2) {
 		left = json_parse_primary_expr(ctx, json_array_get(root, 0));
+		if (!left) {
+			json_error(ctx, "Failed to parse LHS of binop expression.");
+			return NULL;
+		}
 		right = json_parse_primary_expr(ctx, json_array_get(root, 1));
+		if (!right) {
+			json_error(ctx, "Failed to parse RHS of binop expression.");
+			expr_free(left);
+			return NULL;
+		}
 		left = binop_expr_alloc(int_loc, thisop, left, right);
 		for (i = 2; i < json_array_size(root); i++) {
 			jright = json_array_get(root, i);
 			right = json_parse_primary_expr(ctx, jright);
+			if (!right) {
+				json_error(ctx, "Failed to parse RHS of binop expression.");
+				expr_free(left);
+				return NULL;
+			}
 			left = binop_expr_alloc(int_loc, thisop, left, right);
 		}
 		return left;