linux-kernel - [PATCH 5/5] SELinux: Check against union label for file operations

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Message-ID: <20150928200113.8141.56806.stgit@warthog.procyon.org.uk>
Date:	Mon, 28 Sep 2015 21:01:13 +0100
From:	David Howells <dhowells@...hat.com>
To:	linux-unionfs@...r.kernel.org, selinux@...ho.nsa.gov
Cc:	mjg59@...f.ucam.org, dwalsh@...hat.com,
	linux-kernel@...r.kernel.org, eparis@...hat.com,
	dhowells@...hat.com, linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, sds@...ho.nsa.gov
Subject: [PATCH 5/5] SELinux: Check against union label for file operations

File operations (eg. read, write) issued against a file that is attached to
the lower layer of a union file needs to be checked against the union-layer
label not the lower layer label.

The union label is stored in the file_security_struct rather than being
retrieved from one of the inodes.

Signed-off-by: David Howells <dhowells@...hat.com>
---

 security/selinux/hooks.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 522b070d9e2b..ecc883b6d463 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1682,6 +1682,7 @@ static int file_has_perm(const struct cred *cred,
 			 struct file *file,
 			 u32 av)
 {
+	struct inode_security_struct *isec;
 	struct file_security_struct *fsec = file->f_security;
 	struct inode *inode = file_inode(file);
 	struct common_audit_data ad;
@@ -1702,8 +1703,15 @@ static int file_has_perm(const struct cred *cred,
 
 	/* av is zero if only checking access to the descriptor. */
 	rc = 0;
-	if (av)
-		rc = inode_has_perm(cred, inode, av, &ad);
+	if (av && likely(!IS_PRIVATE(inode))) {
+		if (fsec->union_isid) {
+			isec = inode->i_security;
+			rc = avc_has_perm(sid, fsec->union_isid, isec->sclass,
+					  av, &ad);
+		}
+		if (!rc)
+			rc = inode_has_perm(cred, inode, av, &ad);
+	}
 
 out:
 	return rc;

--
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