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>

diff --git a/src/parser_json.c b/src/parser_json.c
index e8fed0d254a5eee5545283c160af3b76ebdee021..c7649ccf5da35ad9a3ac4fc7bd5b30425fd7c15d 100644 (file)
--- 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;