The rclone core does not sanitise ".." in an object's Remote(). Such a name can
arrive from a malicious or buggy backend - an object store permits keys
containing ".." or a leading "/" - and, if acted on, lets a listing or transfer
escape the configured root. A source object named "../../other/x" is copied to
"other/x" outside the destination root, and a crafted listing name surfaces
outside the directory being listed.
Add list.RemoteEscapesRoot, which reports whether a Remote climbs above the
root when joined onto it, and list.RemoveEscaping, which drops and logs such
entries.
Apply RemoveEscaping unconditionally - independent of the include/exclude
filters - at the three per-entry filtering points every listing passes through:
filterDir, walk.listR and walk.walkRDirTree (recursive ListR).
operations.StatJSON calls List and NewObject directly, bypassing those, so it
rejects an escaping remote up front.
This confines every backend at once, so no per-backend change is needed.
Nick Craig-Wood
935197b062