selinux: adjust rules for ATTR_FORCE

As suggested by OGAWA Hirofumi in thread:
http://lkml.org/lkml/2009/8/7/132, we should let selinux_inode_setattr()
to match our ATTR_* rules.  ATTR_FORCE should not force things like
ATTR_SIZE.

[hirofumi@mail.parknet.co.jp: tweaks]
Signed-off-by: WANG Cong <amwang@redhat.com>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: Eric Paris <eparis@redhat.com>
Cc: Eugene Teo <eteo@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Acked-by: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: James Morris <jmorris@namei.org>

security/selinux/hooks.c

@@ -2711,12 +2711,18 @@ static int selinux_inode_permission(struct inode *inode, int mask)
 static int selinux_inode_setattr(struct dentry *dentry, struct iattr *iattr)
 {
 	const struct cred *cred = current_cred();
+	unsigned int ia_valid = iattr->ia_valid;
+
+	/* ATTR_FORCE is just used for ATTR_KILL_S[UG]ID. */
+	if (ia_valid & ATTR_FORCE) {
+		ia_valid &= ~(ATTR_KILL_SUID | ATTR_KILL_SGID | ATTR_MODE |
+			      ATTR_FORCE);
+		if (!ia_valid)
+			return 0;
+	}
 
-	if (iattr->ia_valid & ATTR_FORCE)
-		return 0;
-
-	if (iattr->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID |
-			       ATTR_ATIME_SET | ATTR_MTIME_SET))
+	if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID |
+			ATTR_ATIME_SET | ATTR_MTIME_SET | ATTR_TIMES_SET))
 		return dentry_has_perm(cred, NULL, dentry, FILE__SETATTR);
 
 	return dentry_has_perm(cred, NULL, dentry, FILE__WRITE);