From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8816BC433E2 for ; Thu, 25 Mar 2021 12:22:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4CF9761A1F for ; Thu, 25 Mar 2021 12:22:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230295AbhCYMVd (ORCPT ); Thu, 25 Mar 2021 08:21:33 -0400 Received: from mail.kernel.org ([198.145.29.99]:36636 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229981AbhCYMVS (ORCPT ); Thu, 25 Mar 2021 08:21:18 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 92C7E619C7; Thu, 25 Mar 2021 12:21:15 +0000 (UTC) Date: Thu, 25 Mar 2021 13:21:12 +0100 From: Christian Brauner To: Roberto Sassu Cc: "zohar@linux.ibm.com" , "mjg59@google.com" , "agruenba@redhat.com" , "linux-integrity@vger.kernel.org" , "linux-security-module@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v4 08/11] evm: Allow setxattr() and setattr() for unmodified metadata Message-ID: <20210325122112.htkwkt3emura5day@wittgenstein> References: <20210305151923.29039-1-roberto.sassu@huawei.com> <20210305151923.29039-9-roberto.sassu@huawei.com> <20210325121341.q2ufjhnqe3osjc7c@wittgenstein> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210325121341.q2ufjhnqe3osjc7c@wittgenstein> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 25, 2021 at 01:13:41PM +0100, Christian Brauner wrote: > On Thu, Mar 25, 2021 at 10:53:43AM +0000, Roberto Sassu wrote: > > > From: Roberto Sassu > > > Sent: Friday, March 5, 2021 4:19 PM > > > With the patch to allow xattr/attr operations if a portable signature > > > verification fails, cp and tar can copy all xattrs/attrs so that at the > > > end of the process verification succeeds. > > > > > > However, it might happen that the xattrs/attrs are already set to the > > > correct value (taken at signing time) and signature verification succeeds > > > before the copy has completed. For example, an archive might contains files > > > owned by root and the archive is extracted by root. > > > > > > Then, since portable signatures are immutable, all subsequent operations > > > fail (e.g. fchown()), even if the operation is legitimate (does not alter > > > the current value). > > > > > > This patch avoids this problem by reporting successful operation to user > > > space when that operation does not alter the current value of xattrs/attrs. > > > > > > Signed-off-by: Roberto Sassu > > > --- > > > security/integrity/evm/evm_main.c | 96 > > > +++++++++++++++++++++++++++++++ > > > 1 file changed, 96 insertions(+) > > > > > > diff --git a/security/integrity/evm/evm_main.c > > > b/security/integrity/evm/evm_main.c > > > index eab536fa260f..a07516dcb920 100644 > > > --- a/security/integrity/evm/evm_main.c > > > +++ b/security/integrity/evm/evm_main.c > > > @@ -18,6 +18,7 @@ > > > #include > > > #include > > > #include > > > +#include > > > > > > #include > > > #include > > > @@ -328,6 +329,79 @@ static enum integrity_status > > > evm_verify_current_integrity(struct dentry *dentry) > > > return evm_verify_hmac(dentry, NULL, NULL, 0, NULL); > > > } > > > > > > +/* > > > + * evm_xattr_acl_change - check if passed ACL changes the inode mode > > > + * @dentry: pointer to the affected dentry > > > + * @xattr_name: requested xattr > > > + * @xattr_value: requested xattr value > > > + * @xattr_value_len: requested xattr value length > > > + * > > > + * Check if passed ACL changes the inode mode, which is protected by > > > EVM. > > > + * > > > + * Returns 1 if passed ACL causes inode mode change, 0 otherwise. > > > + */ > > > +static int evm_xattr_acl_change(struct dentry *dentry, const char > > > *xattr_name, > > > + const void *xattr_value, size_t > > > xattr_value_len) > > > +{ > > > + umode_t mode; > > > + struct posix_acl *acl = NULL, *acl_res; > > > + struct inode *inode = d_backing_inode(dentry); > > > + int rc; > > > + > > > + /* UID/GID in ACL have been already converted from user to init ns > > > */ > > > + acl = posix_acl_from_xattr(&init_user_ns, xattr_value, > > > xattr_value_len); > > > + if (!acl) > > > > Based on Mimi's review, I will change this to: > > > > if (IS_ERR_OR_NULL(acl)) > > > > > + return 1; > > > + > > > + acl_res = acl; > > > + rc = posix_acl_update_mode(&init_user_ns, inode, &mode, > > > &acl_res); > > > > About this part, probably it is not correct. > > > > I'm writing a test for this patch that checks if operations > > that don't change the file mode succeed and those that > > do fail. > > > > mount-idmapped --map-mount b:3001:0:1 /mnt /mnt-idmapped > > pushd /mnt > > echo "test" > test-file > > chown 3001 test-file > > chgrp 3001 test-file > > chmod 2644 test-file > > > > setfacl --set u::rw,g::r,o::r,m:r test-file (expected to succeed, caller has CAP_FSETID, so S_ISGID is not dropped) > > setfacl --set u::rw,g::r,o::r,m:rw test-file (expected to fail) > > pushd /mnt-idmapped > > capsh --drop=cap_fsetid -- -c setfacl --set u::rw,g::r,o::r test-file (expected to succeed, caller is in the owning group of test-file, so S_ISGID is not dropped) > > > > After adding a debug line in posix_acl_update_mode(): > > printk("%s: %d(%d) %d\n", __func__, in_group_p(i_gid_into_mnt(mnt_userns, inode)), __kgid_val(i_gid_into_mnt(mnt_userns, inode)), capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID)); > > > > without passing mnt_userns: > > [ 748.262582] setfacl --set u::rw,g::r,o::r,m:r test-file > > [ 748.268021] posix_acl_update_mode: 0(3001) 1 > > [ 748.268035] posix_acl_update_mode: 0(3001) 1 > > [ 748.268570] setfacl --set u::rw,g::r,o::r,m:rw test-file > > [ 748.274193] posix_acl_update_mode: 0(3001) 1 > > [ 748.279198] capsh --drop=cap_fsetid -- -c setfacl --set u::rw,g::r,o::r test-file > > [ 748.287894] posix_acl_update_mode: 0(3001) 0 > > > > passing mnt_userns: > > [ 81.159766] setfacl --set u::rw,g::r,o::r,m:r test-file > > [ 81.165207] posix_acl_update_mode: 0(3001) 1 > > [ 81.165226] posix_acl_update_mode: 0(3001) 1 > > [ 81.165732] setfacl --set u::rw,g::r,o::r,m:rw test-file > > [ 81.170978] posix_acl_update_mode: 0(3001) 1 > > [ 81.176014] capsh --drop=cap_fsetid -- -c setfacl --set u::rw,g::r,o::r test-file > > [ 81.184648] posix_acl_update_mode: 1(0) 0 > > [ 81.184663] posix_acl_update_mode: 1(0) 0 > > > > The difference is that, by passing mnt_userns, the caller (root) is > > in the owning group of the file (3001 -> 0). Without passing mnt_userns, > > it is not (3001 -> 3001). > > > > Christian, Andreas, could you confirm that this is correct? > > Hey Robert, s/Robert/Roberto/ Sorry for the typo.