From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from out03.mta.xmission.com ([166.70.13.233]:58514 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750931AbdADEY4 (ORCPT ); Tue, 3 Jan 2017 23:24:56 -0500 From: ebiederm@xmission.com (Eric W. Biederman) To: Luis Ressel Cc: Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org References: <20161227112037.015dc5ac@gentp.lnet> Date: Wed, 04 Jan 2017 17:20:11 +1300 In-Reply-To: <20161227112037.015dc5ac@gentp.lnet> (Luis Ressel's message of "Tue, 27 Dec 2016 11:20:37 +0100") Message-ID: <87a8b7318k.fsf@xmission.com> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: mount_pseudo(), sget() and MS_KERNMOUNT Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Luis Ressel writes: > Hello, > > With Linux 4.8, the sget() function in fs/super.c got a new permission > check: It now returns -EPERM if > (!(flags & MS_KERNMOUNT) && !ns_capable(user_ns, CAP_SYS_ADMIN)) . > > I presume the first half is intented to detect in-kernel mounts? If so, > why doesn't mount_pseudo() (in fs/libfs.c) pass the MS_KERNMOUNT flag > to sget()? It looks like an oversight that has simply not mattered. > This behaviour has caused a problem for me: During graphics driver > initalization, drm_fs_inode_new() (in drivers/gpu/drm/drm_drv.c) calls > simple_pin_fs(). The MS_KERNMOUNT flag is indeed passed down the > call chain from there, but it is lost when mount_pseudo() is called, as > that function doesn't take a 'flags' argument. > > Hence, the first part of the above permission check fails. (The second > part also fails under some cicumstances due to a SELinux quirk, and > therefore the initalization of my graphics driver doesn't succeed.) I am concerned that perhaps there is some wrong context in here that is causing SELinux to have problems. Does this correct your symptoms? Eric diff --git a/fs/libfs.c b/fs/libfs.c index e973cd51f126..28d6f35feed6 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -245,7 +245,8 @@ struct dentry *mount_pseudo_xattr(struct file_system_type *fs_type, char *name, struct inode *root; struct qstr d_name = QSTR_INIT(name, strlen(name)); - s = sget(fs_type, NULL, set_anon_super, MS_NOUSER, NULL); + s = sget_userns(fs_type, NULL, set_anon_super, MS_KERNMOUNT|MS_NOUSER, + &init_user_ns, NULL); if (IS_ERR(s)) return ERR_CAST(s);