Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752633AbdHPRgj (ORCPT ); Wed, 16 Aug 2017 13:36:39 -0400 Received: from mga07.intel.com ([134.134.136.100]:3324 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752592AbdHPRgh (ORCPT ); Wed, 16 Aug 2017 13:36:37 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.41,383,1498546800"; d="scan'208";a="1163285880" From: Ross Zwisler To: Andrew Morton , linux-kernel@vger.kernel.org Cc: Ross Zwisler , Alexander Viro , Christoph Hellwig , Dan Williams , Dave Chinner , Jan Kara , Matthew Wilcox , linux-fsdevel@vger.kernel.org, linux-nvdimm@lists.01.org, Kees Cook , Will Deacon , Catalin Marinas , Robin Murphy , Mark Rutland Subject: [PATCH] dax: explain how read(2)/write(2) addresses are validated Date: Wed, 16 Aug 2017 11:36:15 -0600 Message-Id: <20170816173615.10098-1-ross.zwisler@linux.intel.com> X-Mailer: git-send-email 2.9.5 In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1158 Lines: 33 Add a comment explaining how the user addresses provided to read(2) and write(2) are validated in the DAX I/O path. We call dax_copy_from_iter() or copy_to_iter() on these without calling access_ok() first in the DAX code, and there was a concern that the user might be able to read/write to arbitrary kernel addresses with this path. Signed-off-by: Ross Zwisler --- Adding a comment instead of adding redundant access_ok() calls in the DAX code. If this is the wrong path to take, please let me know. fs/dax.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/fs/dax.c b/fs/dax.c index 8c67517..2d50f32 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -1060,6 +1060,11 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data, if (map_len > end - pos) map_len = end - pos; + /* + * The userspace address for the memory copy has already been + * validated via access_ok() in either vfs_read() or + * vfs_write(), depending on which operation we are doing. + */ if (iov_iter_rw(iter) == WRITE) map_len = dax_copy_from_iter(dax_dev, pgoff, kaddr, map_len, iter); -- 2.9.5