blockdev: Error out on negative throttling option values

extract_common_blockdev_options() uses qemu_opt_get_number() to parse
the bps/iops numbers to uint64_t, then converts to double and stores in
ThrottleConfig.  The actual parsing is done by strtoull() in
parse_option_number().  Negative numbers are wrapped to large positive
ones, and stored.

We used to reject negative numbers since 7d81c1413c, but this regressed
when the option parsing code was changed later. Now fix this again.

This time, define an arbitrary large upper limit (1e15),  and check the
values so both negative and impractically big numbers are caught and
reported.

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

blockdev.c

@@ -348,7 +348,8 @@ static bool check_throttle_config(ThrottleConfig *cfg, Error **errp)
     }
 
     if (!throttle_is_valid(cfg)) {
-        error_setg(errp, "bps/iops/maxs values must be 0 or greater");
+        error_setg(errp, "bps/iops/max values must be within [0, %lld]",
+                   THROTTLE_VALUE_MAX);
         return false;
     }
 

include/qemu/throttle.h

@@ -29,6 +29,8 @@
 #include "qemu-common.h"
 #include "qemu/timer.h"
 
+#define THROTTLE_VALUE_MAX 1000000000000000LL
+
 typedef enum {
     THROTTLE_BPS_TOTAL,
     THROTTLE_BPS_READ,

util/throttle.c

@@ -282,22 +282,18 @@ bool throttle_conflicting(ThrottleConfig *cfg)
  */
 bool throttle_is_valid(ThrottleConfig *cfg)
 {
-    bool invalid = false;
     int i;
 
     for (i = 0; i < BUCKETS_COUNT; i++) {
-        if (cfg->buckets[i].avg < 0) {
-            invalid = true;
+        if (cfg->buckets[i].avg < 0 ||
+            cfg->buckets[i].max < 0 ||
+            cfg->buckets[i].avg > THROTTLE_VALUE_MAX ||
+            cfg->buckets[i].max > THROTTLE_VALUE_MAX) {
+            return false;
         }
     }
 
-    for (i = 0; i < BUCKETS_COUNT; i++) {
-        if (cfg->buckets[i].max < 0) {
-            invalid = true;
-        }
-    }
-
-    return !invalid;
+    return true;
 }
 
 /* check if bps_max/iops_max is used without bps/iops