test(vmm): add regression test for virtio device write_config()

The test makes sure that a large offset value
does not cause an overflow inside
VirtioDevice::write_config().

Signed-off-by: Nikita Kalyazin <[email protected]>

Author: kalyazin

src/vmm/src/devices/virtio/balloon/device.rs

@@ -762,6 +762,12 @@ pub(crate) mod tests {
         // Make sure nothing got written.
         balloon.read_config(0, &mut actual_config_space);
         assert_eq!(actual_config_space, expected_config_space);
+
+        // Large offset that may cause an overflow.
+        balloon.write_config(u64::MAX, &new_config_space);
+        // Make sure nothing got written.
+        balloon.read_config(0, &mut actual_config_space);
+        assert_eq!(actual_config_space, expected_config_space);
     }
 
     #[test]

src/vmm/src/devices/virtio/block/device.rs

@@ -755,6 +755,12 @@ mod tests {
         // Make sure nothing got written.
         block.read_config(0, &mut actual_config_space);
         assert_eq!(actual_config_space, expected_config_space);
+
+        // Large offset that may cause an overflow.
+        block.write_config(u64::MAX, &new_config_space);
+        // Make sure nothing got written.
+        block.read_config(0, &mut actual_config_space);
+        assert_eq!(actual_config_space, expected_config_space);
     }
 
     #[test]

src/vmm/src/devices/virtio/net/device.rs

@@ -998,6 +998,13 @@ pub mod tests {
         new_config_read = [0u8; MAC_ADDR_LEN];
         net.read_config(0, &mut new_config_read);
         assert_eq!(new_config, new_config_read);
+
+        // Large offset that may cause an overflow.
+        net.write_config(u64::MAX, &new_config);
+        // Verify old config was untouched.
+        new_config_read = [0u8; MAC_ADDR_LEN];
+        net.read_config(0, &mut new_config_read);
+        assert_eq!(new_config, new_config_read);
     }
 
     #[test]