On Wed, Jul 22, 2020 at 02:02:05PM +0100, Stefan Hajnoczi wrote: > virtiofsd cannot run in an unprivileged container because CAP_SYS_ADMIN > is required to create namespaces. > > Introduce a weaker sandbox that is sufficient in container environments > because the container runtime already sets up namespaces. Use chroot to > restrict path traversal to the shared directory. > > virtiofsd loses the following: > > 1. Mount namespace. The process chroots to the shared directory but > leaves the mounts in place. Seccomp rejects mount(2)/umount(2) > syscalls. > > 2. Pid namespace. This should be fine because virtiofsd is the only > process running in the container. > > 3. Network namespace. This should be fine because seccomp already > rejects the connect(2) syscall, but an additional layer of security > is lost. Container runtime-specific network security policies can be > used drop network traffic (except for the vhost-user UNIX domain > socket).
IIUC this relies on the fact that the container will still have CAP_SYS_CHROOT IOW, we still don't have a solution for running virtiofsd as an unprivileged user. Bearing in mind possibly need for future improvements to handle unprivileged users.... > Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com> > --- > tools/virtiofsd/helper.c | 3 +++ > tools/virtiofsd/passthrough_ll.c | 44 ++++++++++++++++++++++++++++++-- > 2 files changed, 45 insertions(+), 2 deletions(-) > > diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c > index 3105b6c23a..7421c9ca1a 100644 > --- a/tools/virtiofsd/helper.c > +++ b/tools/virtiofsd/helper.c > @@ -151,6 +151,9 @@ void fuse_cmdline_help(void) > " -o cache=<mode> cache mode. could be one of > \"auto, " > "always, none\"\n" > " default: auto\n" > + " -o chroot|no_chroot use container-friendly chroot > instead\n" > + " of stronger mount namespace > sandbox\n" > + " default: false\n" A simple boolean like this feels like it lacks future-proofing. Should we have an option that takes an enumerated arg string: -o sandbox=[namespace|chroot|....] so we can add more options later with the same syntax. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
