From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: ebiederm@xmission.com (Eric W. Biederman) To: Seth Forshee Cc: Linux Containers , linux-fsdevel@vger.kernel.org, "Serge E. Hallyn" , Christian Brauner , linux-kernel@vger.kernel.org References: <87o9h6554f.fsf@xmission.com> <20180523232538.4880-2-ebiederm@xmission.com> <20180524135517.GQ3401@ubuntu-xps13> Date: Thu, 24 May 2018 11:55:45 -0500 In-Reply-To: <20180524135517.GQ3401@ubuntu-xps13> (Seth Forshee's message of "Thu, 24 May 2018 08:55:17 -0500") Message-ID: <87y3g92dta.fsf@xmission.com> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [REVIEW][PATCH 2/6] vfs: Allow userns root to call mknod on owned filesystems. Sender: linux-kernel-owner@vger.kernel.org List-ID: Seth Forshee writes: > On Wed, May 23, 2018 at 06:25:34PM -0500, Eric W. Biederman wrote: >> These filesystems already always set SB_I_NODEV so mknod will not be >> useful for gaining control of any devices no matter their permissions. >> This will allow overlayfs and applications to fakeroot to use device >> nodes to represent things on disk. >> >> Signed-off-by: "Eric W. Biederman" > > For a normal filesystem this does seem safe enough. > > However, I'd also like to see us allow unprivileged mounting for > overlayfs, and there we need to worry about whether this would allow a > mknod in an underlying filesystem which should not be allowed. That > mknod will be subject to this same check in the underlying filesystem > using the credentials of the user that mounted the overaly fs, which > should be sufficient to ensure that the mknod is permitted. Sufficient to ensure the mknod is not permitted on the underlying filesystem. I believe you mean. > Thus this looks okay to me. > > Acked-by: Seth Forshee Eric