selinux: simplify away security_policydb_len()

Remove the security_policydb_len() calls from sel_open_policy() and
instead update the inode size from the size returned from
security_read_policy().

Since after this change security_policydb_len() is only called from
security_load_policy(), remove it entirely and just open-code it there.

Also, since security_load_policy() is always called with policy_mutex
held, make it dereference the policy pointer directly and drop the
unnecessary RCU locking.

Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Acked-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

Author: WOnder93

security/selinux/include/security.h

@@ -219,7 +219,6 @@ void selinux_policy_cancel(struct selinux_state *state,
 			struct selinux_policy *policy);
 int security_read_policy(struct selinux_state *state,
 			 void **data, size_t *len);
-size_t security_policydb_len(struct selinux_state *state);
 
 int security_policycap_supported(struct selinux_state *state,
 				 unsigned int req_cap);

security/selinux/selinuxfs.c

@@ -415,16 +415,16 @@ static int sel_open_policy(struct inode *inode, struct file *filp)
 	if (!plm)
 		goto err;
 
-	if (i_size_read(inode) != security_policydb_len(state)) {
-		inode_lock(inode);
-		i_size_write(inode, security_policydb_len(state));
-		inode_unlock(inode);
-	}
-
 	rc = security_read_policy(state, &plm->data, &plm->len);
 	if (rc)
 		goto err;
 
+	if ((size_t)i_size_read(inode) != plm->len) {
+		inode_lock(inode);
+		i_size_write(inode, plm->len);
+		inode_unlock(inode);
+	}
+
 	fsi->policy_opened = 1;
 
 	filp->private_data = plm;

security/selinux/ss/services.c

@@ -2328,22 +2328,6 @@ int security_load_policy(struct selinux_state *state, void *data, size_t len,
 	return rc;
 }
 
-size_t security_policydb_len(struct selinux_state *state)
-{
-	struct selinux_policy *policy;
-	size_t len;
-
-	if (!selinux_initialized(state))
-		return 0;
-
-	rcu_read_lock();
-	policy = rcu_dereference(state->policy);
-	len = policy->policydb.len;
-	rcu_read_unlock();
-
-	return len;
-}
-
 /**
  * security_port_sid - Obtain the SID for a port.
  * @protocol: protocol number
@@ -3903,23 +3887,20 @@ int security_read_policy(struct selinux_state *state,
 	int rc;
 	struct policy_file fp;
 
-	if (!selinux_initialized(state))
+	policy = rcu_dereference_protected(
+			state->policy, lockdep_is_held(&state->policy_mutex));
+	if (!policy)
 		return -EINVAL;
 
-	*len = security_policydb_len(state);
-
+	*len = policy->policydb.len;
 	*data = vmalloc_user(*len);
 	if (!*data)
 		return -ENOMEM;
 
 	fp.data = *data;
 	fp.len = *len;
 
-	rcu_read_lock();
-	policy = rcu_dereference(state->policy);
 	rc = policydb_write(&policy->policydb, &fp);
-	rcu_read_unlock();
-
 	if (rc)
 		return rc;