VolumeCopy, VolumeEcShardsCopy and VolumeTailReceiver dial a
caller-supplied source address (SourceDataNode / SourceVolumeServer)
with no endpoint validation, so an anonymous caller could aim the volume
server at loopback, link-local (cloud metadata) or other unintended
destinations and read dial behavior back as a connectivity oracle.
Apply the same peer-target deny list FetchAndWriteNeedle uses for
replica targets: the source must be a bare host:port whose host is not
loopback, link-local or unspecified; cluster peers stay reachable on
private networks, and -volume.allowUntrustedRemoteEndpoints opts out.
The loopback-using copy tests set the flag to keep exercising the copy
path in process.
Chris Lu
39a8d3253c