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Thu, 23 Jul 2020 13:56:04 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id B32452204C7; Thu, 23 Jul 2020 09:56:03 -0400 (EDT) Date: Thu, 23 Jul 2020 09:56:03 -0400 From: Vivek Goyal To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Subject: Re: [Virtio-fs] [PATCH for-5.1 3/3] virtiofsd: probe unshare(CLONE_FS) and print an error Message-ID: <20200723135603.GB5885@redhat.com> References: <20200722130206.224898-1-stefanha@redhat.com> <20200722130206.224898-4-stefanha@redhat.com> <20200722170328.GU2324845@redhat.com> <20200723124611.GL186372@stefanha-x1.localdomain> <20200723125035.GH2615312@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200723125035.GH2615312@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=vgoyal@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.120; envelope-from=vgoyal@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/22 22:13:02 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 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: , Cc: virtio-fs@redhat.com, rmohr@redhat.com, qemu-devel@nongnu.org, Stefan Hajnoczi , vromanso@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Jul 23, 2020 at 01:50:35PM +0100, Daniel P. Berrangé wrote: > On Thu, Jul 23, 2020 at 01:46:11PM +0100, Stefan Hajnoczi wrote: > > On Wed, Jul 22, 2020 at 06:03:28PM +0100, Daniel P. Berrangé wrote: > > > On Wed, Jul 22, 2020 at 02:02:06PM +0100, Stefan Hajnoczi wrote: > > > > An assertion failure is raised during request processing if > > > > unshare(CLONE_FS) fails. Implement a probe at startup so the problem can > > > > be detected right away. > > > > > > > > Unfortunately Docker/Moby does not include unshare in the seccomp.json > > > > list unless CAP_SYS_ADMIN is given. Other seccomp.json lists always > > > > include unshare (e.g. podman is unaffected): > > > > https://raw.githubusercontent.com/seccomp/containers-golang/master/seccomp.json > > > > > > > > Use "docker run --security-opt seccomp=path/to/seccomp.json ..." if the > > > > default seccomp.json is missing unshare. > > > > > > > > Cc: Misono Tomohiro > > > > Signed-off-by: Stefan Hajnoczi > > > > --- > > > > tools/virtiofsd/fuse_virtio.c | 13 +++++++++++++ > > > > 1 file changed, 13 insertions(+) > > > > > > > > diff --git a/tools/virtiofsd/fuse_virtio.c b/tools/virtiofsd/fuse_virtio.c > > > > index 3b6d16a041..ebeb352514 100644 > > > > --- a/tools/virtiofsd/fuse_virtio.c > > > > +++ b/tools/virtiofsd/fuse_virtio.c > > > > @@ -949,6 +949,19 @@ int virtio_session_mount(struct fuse_session *se) > > > > { > > > > int ret; > > > > > > > > + /* > > > > + * Test that unshare(CLONE_FS) works. fv_queue_worker() will need it. It's > > > > + * an unprivileged system call but some Docker/Moby versions are known to > > > > + * reject it via seccomp when CAP_SYS_ADMIN is not given. > > > > + */ > > > > + ret = unshare(CLONE_FS); > > > > + if (ret == -1 && errno == EPERM) { > > > > + fuse_log(FUSE_LOG_ERR, "unshare(CLONE_FS) failed with EPERM. If " > > > > + "running in a container please check that the container " > > > > + "runtime seccomp policy allows unshare.\n"); > > > > + return -1; > > > > + } > > > > + > > > > > > This describes the unshare() call as a "probe" and a "test", but that's > > > misleading IMHO. A "probe" / "test" implies that after it has completed, > > > there's no lingering side-effect, which isn't the case here. > > > > > > This is actively changing the process' namespace environment in the > > > success case, and not putting it back how it was originally. > > > > > > May be this is in fact OK, but if so I think the commit message and > > > comment should explain/justify what its fine to have this lingering > > > side-effect. > > > > > > If we want to avoid the side-effect then we need to fork() and run > > > unshare() in the child, and use a check of exit status of the child > > > to determine the result. > > > > Thanks for pointing this out. I'll add a comment explaining that > > virtiofsd is single-threaded at this point. No other threads share the > > file system attributes so the call has no observable side-effects. > > Also, if we do an unshare() here, do we still need the unshare() later > on in the code ? I think so. That unshare() later is to isolate one thread from other. Thanks Vivek