From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932141AbaKEPnT (ORCPT ); Wed, 5 Nov 2014 10:43:19 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45217 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755175AbaKEPnO (ORCPT ); Wed, 5 Nov 2014 10:43:14 -0500 Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 Subject: [PATCH 5/7] SELinux: Handle opening of a unioned file From: David Howells To: linux-unionfs@vger.kernel.org, selinux@tycho.nsa.gov Cc: dhowells@redhat.com, linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Date: Wed, 05 Nov 2014 15:43:07 +0000 Message-ID: <20141105154307.2555.9847.stgit@warthog.procyon.org.uk> In-Reply-To: <20141105154217.2555.578.stgit@warthog.procyon.org.uk> References: <20141105154217.2555.578.stgit@warthog.procyon.org.uk> User-Agent: StGit/0.17-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Handle the opening of a unioned file by trying to derive the label that would be attached to the union-layer inode if it doesn't exist. If the union-layer inode does exist (as it necessarily does in overlayfs, but not in unionmount), we assume that it has the right label and use that. Otherwise we try to get it from the superblock. If the superblock has a globally-applied label, we use that, otherwise we try to transition to an appropriate label. This union label is then stored in the file_security_struct. We then perform an additional check to make sure that the calling task is granted permission by the union-layer inode label to open the file in addition to a check to make sure that the task is granted permission to open the lower file with the lower inode label. Signed-off-by: David Howells --- security/selinux/hooks.c | 56 +++++++++++++++++++++++++++++++++++++ security/selinux/include/objsec.h | 1 + 2 files changed, 57 insertions(+) diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 6fd8090cc7a5..f43f07fdc028 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -3431,6 +3431,58 @@ static int selinux_file_receive(struct file *file) return file_has_perm(cred, file, file_to_av(file)); } +/* + * We have a file opened on a unioned file system that falls through to a file + * on a lower layer. If there is a union inode, we try to get the label from + * that, otherwise we need to get it from the superblock. + */ +static int selinux_file_open_union(struct file *file, + const struct path *union_path, + struct file_security_struct *fsec, + const struct cred *cred) +{ + const struct superblock_security_struct *sbsec; + const struct inode_security_struct *isec, *dsec; + const struct task_security_struct *tsec = current_security(); + struct common_audit_data ad; + const struct inode *inode = union_path->dentry->d_inode; + struct dentry *dir; + int rc; + + sbsec = union_path->dentry->d_sb->s_security; + + if (inode) { + isec = inode->i_security; + fsec->union_isid = isec->sid; + } else if ((sbsec->flags & SE_SBINITIALIZED) && + (sbsec->behavior == SECURITY_FS_USE_MNTPOINT)) { + fsec->union_isid = sbsec->mntpoint_sid; + } else { + dir = dget_parent(union_path->dentry); + dsec = dir->d_inode->i_security; + + rc = security_transition_sid( + tsec->sid, dsec->sid, + inode_mode_to_security_class(file_inode(file)->i_mode), + &union_path->dentry->d_name, + &fsec->union_isid); + dput(dir); + if (rc) { + printk(KERN_WARNING "%s: " + "security_transition_sid failed, rc=%d (name=%pD)\n", + __func__, -rc, file); + return rc; + } + } + + /* We need to check that the union file is allowed to be opened as well + * as checking that the lower file is allowed to be opened. + */ + ad.type = LSM_AUDIT_DATA_PATH; + ad.u.path = *union_path; + return inode_has_perm(cred, file_inode(file), fsec->union_isid, &ad); +} + static int selinux_file_open(struct file *file, const struct path *union_path, const struct cred *cred) { @@ -3456,6 +3508,10 @@ static int selinux_file_open(struct file *file, const struct path *union_path, * new inode label or new policy. * This check is not redundant - do not remove. */ + + if (union_path->dentry != file->f_path.dentry) + selinux_file_open_union(file, union_path, fsec, cred); + return file_path_has_perm(cred, file, open_file_to_av(file)); } diff --git a/security/selinux/include/objsec.h b/security/selinux/include/objsec.h index 81fa718d5cb3..f088c080aa9e 100644 --- a/security/selinux/include/objsec.h +++ b/security/selinux/include/objsec.h @@ -54,6 +54,7 @@ struct file_security_struct { u32 sid; /* SID of open file description */ u32 fown_sid; /* SID of file owner (for SIGIO) */ u32 isid; /* SID of inode at the time of file open */ + u32 union_isid; /* SID of would-be inodes in union top (or 0) */ u32 pseqno; /* Policy seqno at the time of file open */ };