From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:50624 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932170AbeCKVwt (ORCPT ); Sun, 11 Mar 2018 17:52:49 -0400 Received: from pps.filterd (m0098394.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w2BLnDMj086806 for ; Sun, 11 Mar 2018 17:52:49 -0400 Received: from e06smtp13.uk.ibm.com (e06smtp13.uk.ibm.com [195.75.94.109]) by mx0a-001b2d01.pphosted.com with ESMTP id 2gmw6nws6y-1 (version=TLSv1.2 cipher=AES256-SHA256 bits=256 verify=NOT) for ; Sun, 11 Mar 2018 17:52:49 -0400 Received: from localhost by e06smtp13.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sun, 11 Mar 2018 21:52:47 -0000 Subject: Re: [PATCH] evm: check for remount ro in progress before writing From: Mimi Zohar To: Sascha Hauer , linux-integrity@vger.kernel.org Date: Sun, 11 Mar 2018 17:52:44 -0400 In-Reply-To: <20180301123845.26189-1-s.hauer@pengutronix.de> References: <20180301123845.26189-1-s.hauer@pengutronix.de> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Message-Id: <1520805164.3547.3.camel@linux.vnet.ibm.com> Sender: linux-integrity-owner@vger.kernel.org List-ID: On Thu, 2018-03-01 at 13:38 +0100, Sascha Hauer wrote: > EVM might update the evm xattr while the VFS performs a remount to > readonly mode. This is not properly checked for, additionally check > the s_readonly_remount superblock flag before writing. > The bug can for example be observed with UBIFS. UBIFS checks the free > space on the device before and after a remount. With EVM enabled the > free space sometimes differs between both checks. > > Signed-off-by: Sascha Hauer > --- > security/integrity/evm/evm_main.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c > index a8d502827270..4a147a998aa7 100644 > --- a/security/integrity/evm/evm_main.c > +++ b/security/integrity/evm/evm_main.c > @@ -185,6 +185,7 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry, > iint->flags |= EVM_IMMUTABLE_DIGSIG; > evm_status = INTEGRITY_PASS_IMMUTABLE; > } else if (!IS_RDONLY(d_backing_inode(dentry)) && > + !(dentry->d_inode->i_sb->s_readonly_remount) && The other 2 conditions are using d_back_inode(). Shouldn't this one be too? Mimi > !IS_IMMUTABLE(d_backing_inode(dentry))) { > evm_update_evmxattr(dentry, xattr_name, > xattr_value,