Messages in this thread | | | From | (Eric W. Biederman) | Date | Tue, 14 Oct 2014 13:01:02 -0700 | Subject | Re: [fuse-devel] [PATCH v4 4/5] fuse: Support privileged xattrs only with a mount option |
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Michael j Theall <mtheall@us.ibm.com> writes:
> Seth Forshee <seth.forshee@canonical.com> wrote on 10/14/2014 09:25:55 AM: > >> From: Seth Forshee <seth.forshee@canonical.com> >> To: Miklos Szeredi <miklos@szeredi.hu> >> Cc: fuse-devel@lists.sourceforge.net, "Serge H. Hallyn" >> <serge.hallyn@ubuntu.com>, linux-kernel@vger.kernel.org, Seth >> Forshee <seth.forshee@canonical.com>, "Eric W. Biederman" >> <ebiederm@xmission.com>, 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
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