From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751005AbdADEY6 (ORCPT ); Tue, 3 Jan 2017 23:24:58 -0500 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> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1cOd7J-0004hk-8N;;;mid=<87a8b7318k.fsf@xmission.com>;;;hst=in02.mta.xmission.com;;;ip=101.100.131.98;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1/zItHOzSVxF+ljUrfzW1WHkmz5L3q3MPo= X-SA-Exim-Connect-IP: 101.100.131.98 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.0 T_TM2_M_HEADER_IN_MSG BODY: No description available. * 0.8 BAYES_50 BODY: Bayes spam probability is 40 to 60% * [score: 0.5000] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa02 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 T_TooManySym_01 4+ unique symbols in subject X-Spam-DCC: XMission; sa02 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Luis Ressel X-Spam-Relay-Country: X-Spam-Timing: total 5344 ms - load_scoreonly_sql: 0.09 (0.0%), signal_user_changed: 12 (0.2%), b_tie_ro: 9 (0.2%), parse: 2.2 (0.0%), extract_message_metadata: 31 (0.6%), get_uri_detail_list: 2.6 (0.0%), tests_pri_-1000: 9 (0.2%), tests_pri_-950: 2.4 (0.0%), tests_pri_-900: 1.96 (0.0%), tests_pri_-400: 38 (0.7%), check_bayes: 36 (0.7%), b_tokenize: 12 (0.2%), b_tok_get_all: 9 (0.2%), b_comp_prob: 6 (0.1%), b_tok_touch_all: 3.7 (0.1%), b_finish: 1.77 (0.0%), tests_pri_0: 418 (7.8%), check_dkim_signature: 1.22 (0.0%), check_dkim_adsp: 6 (0.1%), tests_pri_500: 4820 (90.2%), poll_dns_idle: 4800 (89.8%), rewrite_mail: 0.00 (0.0%) Subject: Re: mount_pseudo(), sget() and MS_KERNMOUNT X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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);