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Message-ID: <20140721143442.GD111224@ubuntu-hedt> Date: Mon, 21 Jul 2014 09:34:42 -0500 From: Seth Forshee <seth.forshee@...onical.com> To: Miklos Szeredi <miklos@...redi.hu> Cc: Kernel Mailing List <linux-kernel@...r.kernel.org>, fuse-devel <fuse-devel@...ts.sourceforge.net>, lxc-devel@...ts.linuxcontainers.org, "Eric W. Biederman" <ebiederm@...ssion.com>, Serge Hallyn <serge.hallyn@...ntu.com>, "Michael H. Warfield" <mhw@...tsend.com>, Seth Forshee <seth.forshee@...onical.com> Subject: Re: [PATCH 3/3] fuse: Allow mounts from user namespaces On Mon, Jul 21, 2014 at 03:09:14PM +0200, Miklos Szeredi wrote: > On Mon, Jul 21, 2014 at 2:47 PM, Seth Forshee > <seth.forshee@...onical.com> wrote: > > On Fri, Jul 18, 2014 at 05:33:23PM +0200, Miklos Szeredi wrote: > >> On Mon, Jul 14, 2014 at 9:18 PM, Seth Forshee > >> <seth.forshee@...onical.com> wrote: > >> > Update fuse to allow mounts from user namespaces. During mount > >> > current_user_ns() is stashed away, > >> > >> Same thing here. While practically this may work, it's theoretically > >> wrong, and possibly may go wrong in special situations. In fuse > >> there's no official "server process", so storing information, like > >> namespace, about one is going to be wrong. > > > > What you're suggesting would probably work fine when dealing with pids. > > It's not going to work though for the checks I've added in > > fuse_allow_current_process() that the process is in the mount owner's > > user ns, and without those checks or something similar I don't think > > it's safe to permit allow_other for user ns mounts. > > You can add that check in fuse_dev_do_read() as well. If the > fsuid/fsgid doesn't exist in the "server's" namespace, then set > req->out.h.error and call request_end(). Okay, that seems like it should work. > > Can you elaborate on what special situations might violate these > > assumptions or otherwise cause problems? > > What's preventing a fuse fs implementation from handling FUSE_INIT in > one process and then handling the rest in a different process > (possibly in a different namespace)? Nothing, but I'm having a hard time imagining why that would ever be useful. The user/group ids passed in the mount options would have to be mapped into that namespace, otherwise all requests will just fail in the check you suggest above. The only thing I can think of would be if someone wanted to proxy mounts trough a process in a more privileged context, but then the main point of these patches is to make that unnecessary. But I also think your approach should work just as well as mine for the use cases that do make sense to me, so I'll go ahead and give it a try. Thanks, Seth -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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