With -l/--links the local backend faithfully recreates a source ".rclonelink" as
a real symlink at the destination. Directory metadata (chmod/chown/chtimes),
however, was applied with the raw following syscalls
os.Chmod/os.Chown/os.Chtimes rather than through the os.Root sandbox used for
content writes. A Directory is never a translatedLink, so when the destination
path already existed as a symlink planted by an untrusted source, the metadata
was applied through it to a target outside the backup destination.
Route directory metadata through os.Root when translating symlinks, so a planted
symlink can no longer redirect chmod/chown/chtimes out of the destination, while
legitimate in-tree directories are unaffected.
Nick Craig-Wood
29bb1e1134