OptsVisitor: don't try to flatten overlong integer ranges

Prevent mistyped command line options from incurring high memory and CPU
usage at startup. 64K elements in a range should be enough for everyone
(TM).

The OPTS_VISITOR_RANGE_MAX macro is public so that unit tests can
construct corner cases with it.
Signed-off-by: NLaszlo Ersek <lersek@redhat.com>
Tested-by: NWanlong Gao <gaowanlong@cn.fujitsu.com>
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>

include/qapi/opts-visitor.h

@@ -16,6 +16,12 @@
 #include "qapi/visitor.h"
 #include "qemu/option.h"
 
+/* Inclusive upper bound on the size of any flattened range. This is a safety
+ * (= anti-annoyance) measure; wrong ranges should not cause long startup
+ * delays nor exhaust virtual memory.
+ */
+#define OPTS_VISITOR_RANGE_MAX 65536
+
 typedef struct OptsVisitor OptsVisitor;
 
 /* Contrarily to qemu-option.c::parse_option_number(), OptsVisitor's "int"

qapi/opts-visitor.c

@@ -384,7 +384,9 @@ opts_type_int(Visitor *v, int64_t *obj, const char *name, Error **errp)
             str = endptr + 1;
             val2 = strtoll(str, &endptr, 0);
             if (errno == 0 && endptr > str && *endptr == '\0' &&
-                INT64_MIN <= val2 && val2 <= INT64_MAX && val <= val2) {
+                INT64_MIN <= val2 && val2 <= INT64_MAX && val <= val2 &&
+                (val > INT64_MAX - OPTS_VISITOR_RANGE_MAX ||
+                 val2 < val + OPTS_VISITOR_RANGE_MAX)) {
                 ov->range_next.s = val;
                 ov->range_limit.s = val2;
                 ov->list_mode = LM_SIGNED_INTERVAL;
@@ -435,7 +437,8 @@ opts_type_uint64(Visitor *v, uint64_t *obj, const char *name, Error **errp)
 
             str = endptr + 1;
             if (parse_uint_full(str, &val2, 0) == 0 &&
-                val2 <= UINT64_MAX && val <= val2) {
+                val2 <= UINT64_MAX && val <= val2 &&
+                val2 - val < OPTS_VISITOR_RANGE_MAX) {
                 ov->range_next.u = val;
                 ov->range_limit.u = val2;
                 ov->list_mode = LM_UNSIGNED_INTERVAL;