Re: [PATCH v3 0/1] Relax restrictions on user.* xattr

On Tue, Sep 14, 2021 at 09:59:19AM -0400, Bruce Fields wrote:

On Tue, Sep 14, 2021 at 8:52 AM Vivek Goyal [off-list ref] wrote:

quoted

Same is the requirement for regular containers and that's why
podman (and possibly other container managers), make top level
storage directory only readable and searchable by root, so that
unpriveleged entities on host can not access container root filesystem
data.

Note--if that directory is on NFS, making it readable and searchable
by root is very weak protection, since it's often possible for an
attacker to guess filehandles and access objects without the need for
directory lookups.

open_by_handle_at() requires CAP_DAC_READ_SEARCH. And if you have
CAP_DAC_READ_SEARCH, you don't need to even guess file handles. You
should be able to read/search through all directories, IIUC.

So how does one make sure that shared directory on host is not
accessible to unprivileged entities. If making directory accessible
to root only is weaker security, what are the options for stronger
security.

Vivek