Re: [PATCH v2 0/3] virtiofsd: allow virtiofsd to run in a container

[Dr. David Alan Gilbert]

* Stefan Hajnoczi (stefanha@redhat.com) wrote:
> v2:
>  * Update virtiofsd.rst documentation on sandboxing modes
>  * Change syntax to -o sandbox=namespace|chroot
>  * Add comment explaining that unshare(CLONE_FS) has no visible side-effect
>    while single-threaded
>  * xfstests and pjdfstest pass. Did not run tests on overlayfs because 
> required
>    xattrs do not work without CAP_SYS_ADMIN.
> 
> Mrunal and Dan: This patch series adds a sandboxing mode where virtiofsd 
> relies
> on the container runtime for isolation. It only does
> chroot("path/to/shared-dir"), seccomp, and drops Linux capabilities. 
> Previously
> it created a new mount, pid, and net namespace but cannot do this without
> CAP_SYS_ADMIN when run inside a container. pivot_root("path/to/shared-dir") 
> has
> been replaced with chroot("path/to/shared-dir"), again because CAP_SYS_ADMIN 
> is
> unavailable. The point of the chroot() is to prevent escapes from the shared
> directory during path traversal. Does this ring any alarm bells or does it
> sound sane?
> 
> Container runtimes handle namespace setup and remove privileges needed by
> virtiofsd to perform sandboxing. Luckily the container environment already
> provides most of the sandbox that virtiofsd needs for security.
> 
> Introduce a new "virtiofsd -o sandbox=chroot" option that uses chroot(2)
> instead of namespaces. This option allows virtiofsd to work inside a 
> container.
> 
> Please see the individual patches for details on the changes and security
> implications.
> 
> Given that people are starting to attempt running virtiofsd in containers I
> think this should go into QEMU 5.1.

I've queued 1 and 3; waiting for someone with better knowledge of chroot
to review 2.

Dave

> Stefan Hajnoczi (3):
>   virtiofsd: drop CAP_DAC_READ_SEARCH
>   virtiofsd: add container-friendly -o sandbox=chroot option
>   virtiofsd: probe unshare(CLONE_FS) and print an error
> 
>  tools/virtiofsd/fuse_virtio.c    | 16 +++++++++
>  tools/virtiofsd/helper.c         |  8 +++++
>  tools/virtiofsd/passthrough_ll.c | 58 ++++++++++++++++++++++++++++++--
>  docs/tools/virtiofsd.rst         | 32 ++++++++++++++----
>  4 files changed, 104 insertions(+), 10 deletions(-)
> 
> -- 
> 2.26.2
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK