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Wed, 22 Jul 2020 16:58:14 +0000 (UTC) Date: Wed, 22 Jul 2020 17:58:11 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Stefan Hajnoczi Subject: Re: [PATCH for-5.1 2/3] virtiofsd: add container-friendly -o chroot sandboxing option Message-ID: <20200722165811.GT2324845@redhat.com> References: <20200722130206.224898-1-stefanha@redhat.com> <20200722130206.224898-3-stefanha@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200722130206.224898-3-stefanha@redhat.com> User-Agent: Mutt/1.14.5 (2020-06-23) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.120; envelope-from=berrange@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/22 00:40:35 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: virtio-fs@redhat.com, vromanso@redhat.com, qemu-devel@nongnu.org, "Dr. David Alan Gilbert" , rmohr@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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 > --- > 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= 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 :|