The Linux kernel already supports per user namespace sandboxed mounts:
21ca59b365c0 ("binfmt_misc: enable sandboxed mounts")
The overall dump/restore logic is based on the fact that a binfmt_misc
superblock is static and is allocated once per a binfmt_misc mount
within a given user namespace. So the code makes a temporary mount to
read/write the entries and then removes it. The binfmt_misc data is
stored to the USERNS image.
Signed-off-by: Dmitry Sepp <dmitry.sepp@virtuozzo.com>
51e1d41a0e