smack: fix access permissions for keyring

Function smack_key_permission() only issues smack requests for the
following operations:
 - KEY_NEED_READ (issues MAY_READ)
 - KEY_NEED_WRITE (issues MAY_WRITE)
 - KEY_NEED_LINK (issues MAY_WRITE)
 - KEY_NEED_SETATTR (issues MAY_WRITE)
A blank smack request is issued in all other cases, resulting in
smack access being granted if there is any rule defined between
subject and object, or denied with -EACCES otherwise.

Request MAY_READ access for KEY_NEED_SEARCH and KEY_NEED_VIEW.
Fix the logic in the unlikely case when both MAY_READ and
MAY_WRITE are needed. Validate access permission field for valid
contents.
Signed-off-by: Zoran Markovic <zmarkovic@sierrawireless.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Cc: Casey Schaufler <casey@schaufler-ca.com>
Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>

security/smack/smack_lsm.c

@@ -4333,6 +4333,12 @@ static int smack_key_permission(key_ref_t key_ref,
 	int request = 0;
 	int rc;
 
+	/*
+	 * Validate requested permissions
+	 */
+	if (perm & ~KEY_NEED_ALL)
+		return -EINVAL;
+
 	keyp = key_ref_to_ptr(key_ref);
 	if (keyp == NULL)
 		return -EINVAL;
@@ -4356,10 +4362,10 @@ static int smack_key_permission(key_ref_t key_ref,
 	ad.a.u.key_struct.key = keyp->serial;
 	ad.a.u.key_struct.key_desc = keyp->description;
 #endif
-	if (perm & KEY_NEED_READ)
-		request = MAY_READ;
+	if (perm & (KEY_NEED_READ | KEY_NEED_SEARCH | KEY_NEED_VIEW))
+		request |= MAY_READ;
 	if (perm & (KEY_NEED_WRITE | KEY_NEED_LINK | KEY_NEED_SETATTR))
-		request = MAY_WRITE;
+		request |= MAY_WRITE;
 	rc = smk_access(tkp, keyp->security, request, &ad);
 	rc = smk_bu_note("key access", tkp, keyp->security, request, rc);
 	return rc;