From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [fuse-devel] [PATCH v4 4/5] fuse: Support privileged xattrs only with a mount option Date: Tue, 14 Oct 2014 13:01:02 -0700 Message-ID: <878ukis9oh.fsf@x220.int.ebiederm.org> References: <1413296756-25071-1-git-send-email-seth.forshee@canonical.com> <1413296756-25071-5-git-send-email-seth.forshee@canonical.com> Mime-Version: 1.0 Content-Type: text/plain Cc: Seth Forshee , fuse-devel@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Miklos Szeredi , "Serge H. Hallyn" To: Michael j Theall Return-path: In-Reply-To: (Michael j. Theall's message of "Tue, 14 Oct 2014 13:12:26 -0500") Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Michael j Theall writes: > Seth Forshee wrote on 10/14/2014 09:25:55 AM: > >> From: Seth Forshee >> To: Miklos Szeredi >> Cc: fuse-devel@lists.sourceforge.net, "Serge H. Hallyn" >> , linux-kernel@vger.kernel.org, Seth >> Forshee , "Eric W. Biederman" >> , linux-fsdevel@vger.kernel.org >> Date: 10/14/2014 09:27 AM >> Subject: [fuse-devel] [PATCH v4 4/5] fuse: Support privileged xattrs >> only with a mount option >> >> Allowing unprivileged users to provide arbitrary xattrs via fuse >> mounts bypasses the normal restrictions on setting xattrs. Such >> mounts should be restricted to reading and writing xattrs in the >> user.* namespace. >> > > Can you explain how the normal restrictions on setting xattrs are > bypassed? If the fuse server is not run by root. Which is a large part of the point of fuse. > My filesystem still needs security.* and system.*, and it looks like > xattr_permission already prevents non-privileged users from accessing > trusted.* If the filesystem is mounted with nosuid (typical of a non-privileged mount of fuse) then the security.* attributes are ignored. >> It's difficult though to tell whether a mount is being performed >> on behalf of an unprivileged user since fuse mounts are ususally >> done via a suid root helper. Thus a new mount option, >> privileged_xattrs, is added to indicated that xattrs from other >> namespaces are allowed. This option can only be supplied by >> system-wide root; supplying the option as an unprivileged user >> will cause the mount to fail. > > I can't say I'm convinced that this is the right direction to head. With respect to defaults we could keep the current default if you have the global CAP_SYS_ADMIN privilege when the mount takes place and then avoid breaking anything. Eric