[Qemu-devel] [PATCH v3] virtio-rng: Add human-readable error message for negative max-bytes parameter

[John Snow]

If a negative integer is used for the max_bytes parameter, QEMU currently
calls abort() and leaves behind a core dump. This patch adds a simple
error message to make the reason for the termination clearer.

There is an underlying insufficiency in the parameter parsing code of QEMU
that renders it unable to reject negative values for unsigned properties,
thus the error message "a non-negative integer below 2^63" is the most
user-friendly and correct message we can give until the underlying 
insufficiency is corrected.

Signed-off-by: John Snow <address@hidden>
---
v3: Adjusted the error message to be more semantically meaningful, but
while acknowledging the limitations of the current unsigned integer
parsing routines.

 hw/virtio/virtio-rng.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/virtio-rng.c b/hw/virtio/virtio-rng.c
index 1356aca..7c5a675 100644
--- a/hw/virtio/virtio-rng.c
+++ b/hw/virtio/virtio-rng.c
@@ -181,7 +181,13 @@ static void virtio_rng_device_realize(DeviceState *dev, 
Error **errp)
 
     vrng->vq = virtio_add_queue(vdev, 8, handle_input);
 
-    assert(vrng->conf.max_bytes <= INT64_MAX);
+    /* Workaround: Property parsing does not enforce unsigned integers,
+     * So this is a hack to reject such numbers. */
+    if (vrng->conf.max_bytes > INT64_MAX) {
+        error_set(errp, QERR_INVALID_PARAMETER_VALUE, "max-bytes",
+                  "a non-negative integer below 2^63");
+        return;
+    }
     vrng->quota_remaining = vrng->conf.max_bytes;
 
     vrng->rate_limit_timer = timer_new_ms(QEMU_CLOCK_VIRTUAL,
-- 
1.9.3