From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752837AbbFNQsW (ORCPT ); Sun, 14 Jun 2015 12:48:22 -0400 Received: from mail-wg0-f49.google.com ([74.125.82.49]:36834 "EHLO mail-wg0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751625AbbFNQsO (ORCPT ); Sun, 14 Jun 2015 12:48:14 -0400 Date: Sun, 14 Jun 2015 09:48:09 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Linus Torvalds cc: Prarit Bhargava , Morten Stevens , Daniel Wagner , Dave Chinner , Eric Paris , Eric Sandeen , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: mm: shmem_zero_setup skip security check and lockdep conflict with XFS Message-ID: User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It appears that, at some point last year, XFS made directory handling changes which bring it into lockdep conflict with shmem_zero_setup(): it is surprising that mmap() can clone an inode while holding mmap_sem, but that has been so for many years. Since those few lockdep traces that I've seen all implicated selinux, I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which v3.13's commit c7277090927a ("security: shmem: implement kernel private shmem inodes") introduced to avoid LSM checks on kernel-internal inodes: the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail. This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero (and MAP_SHARED|MAP_ANONYMOUS). I thought there were also drivers which cloned inode in mmap(), but if so, I cannot locate them now. Reported-and-tested-by: Prarit Bhargava Reported-by: Daniel Wagner Reported-by: Morten Stevens Signed-off-by: Hugh Dickins --- mm/shmem.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) --- 4.1-rc7/mm/shmem.c 2015-04-26 19:16:31.352191298 -0700 +++ linux/mm/shmem.c 2015-06-14 09:26:49.461120166 -0700 @@ -3401,7 +3401,13 @@ int shmem_zero_setup(struct vm_area_stru struct file *file; loff_t size = vma->vm_end - vma->vm_start; - file = shmem_file_setup("dev/zero", size, vma->vm_flags); + /* + * Cloning a new file under mmap_sem leads to a lock ordering conflict + * between XFS directory reading and selinux: since this file is only + * accessible to the user through its mapping, use S_PRIVATE flag to + * bypass file security, in the same way as shmem_kernel_file_setup(). + */ + file = __shmem_file_setup("dev/zero", size, vma->vm_flags, S_PRIVATE); if (IS_ERR(file)) return PTR_ERR(file);