Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754216AbdLDNmf (ORCPT ); Mon, 4 Dec 2017 08:42:35 -0500 Received: from lhrrgout.huawei.com ([194.213.3.17]:64681 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753758AbdLDNmd (ORCPT ); Mon, 4 Dec 2017 08:42:33 -0500 Subject: Re: [PATCHv5 1/1] ima: re-introduce own integrity cache lock To: Mimi Zohar , Dmitry Kasatkin , , CC: , , , Dmitry Kasatkin References: <1512389173.3977.26.camel@linux.vnet.ibm.com> From: Roberto Sassu Message-ID: <37b6f8d7-69a8-8900-e7b6-a614b64f91dd@huawei.com> Date: Mon, 4 Dec 2017 14:42:12 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <1512389173.3977.26.camel@linux.vnet.ibm.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 8bit X-Originating-IP: [10.220.96.228] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3607 Lines: 78 On 12/4/2017 1:06 PM, Mimi Zohar wrote: > Hi Dmitry, > > On Fri, 2017-12-01 at 20:40 +0200, Dmitry Kasatkin wrote: >> The original design was discussed 3+ years ago, but was never completed/upstreamed. >> Based on the recent discussions with Linus >> https://patchwork.kernel.org/patch/9975919, I've rebased this patch. >> >> Before IMA appraisal was introduced, IMA was using own integrity cache >> lock along with i_mutex. process_measurement and ima_file_free took >> the iint->mutex first and then the i_mutex, while setxattr, chmod and >> chown took the locks in reverse order. To resolve the potential deadlock, >> i_mutex was moved to protect entire IMA functionality and the redundant >> iint->mutex was eliminated. >> >> Solution was based on the assumption that filesystem code does not take >> i_mutex further. But when file is opened with O_DIRECT flag, direct-io >> implementation takes i_mutex and produces deadlock. Furthermore, certain >> other filesystem operations, such as llseek, also take i_mutex. >> >> More recently some filesystems have replaced their filesystem specific >> lock with the global i_rwsem to read a file. As a result, when IMA >> attempts to calculate the file hash, reading the file attempts to take >> the i_rwsem again. >> >> To resolve O_DIRECT related deadlock problem, this patch re-introduces >> iint->mutex. But to eliminate the original chmod() related deadlock >> problem, this patch eliminates the requirement for chmod hooks to take >> the iint->mutex by introducing additional atomic iint->attr_flags to >> indicate calling of the hooks. The allowed locking order is to take >> the iint->mutex first and then the i_rwsem. >> >> Original flags were cleared in chmod(), setxattr() or removwxattr() hooks >> and tested when file was closed or opened again. New atomic flags are set >> or cleared in those hooks and tested to clear iint->flags on close or on open. >> >> Atomic flags are following: >> * IMA_CHANGE_ATTR - indicates that chATTR() was called (chmod, chown, chgrp) >> and file attributes have changed. On file open, it causes IMA to clear >> iint->flags to re-evaluate policy and perform IMA functions again. >> * IMA_CHANGE_XATTR - indicates that setxattr or removexattr was called and >> extended attributes have changed. On file open, it causes IMA to clear >> iint->flags IMA_DONE_MASK to re-appraise. >> * IMA_UPDATE_XATTR - indicates that security.ima needs to be updated. >> It is cleared if file policy changes and no update is needed. >> * IMA_DIGSIG - indicates that file security.ima has signature and file >> security.ima must not update to file has on file close. > > Nice!  I've been testing with this patch and all seems good.  Before > queueing this patch to be upstreamed, I'd appreciate if others tested > using it as well.  It applies cleanly to the next-queued branch. If the inode lock is released before the IMA_MEASURE flag is set, the ToMToU violation will not be detected when a writer accesses the same inode. This issue was fixed with commit f7a859ff7395c. Roberto > A subsequent patch will remove the O_DIRECT check in > ima_calc_file_hash(). > > Fixes: Commit 6552321831dc "xfs: remove i_iolock and use i_rwsem in > the VFS inode instead" > > thanks, > > Mimi > > -- > To unsubscribe from this list: send the line "unsubscribe linux-security-module" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Bo PENG, Qiuen PENG, Shengli WANG