selinux: shrink critical section in sel_write_load()

commit 868f31e upstream.

Currently sel_write_load() takes the policy mutex earlier than
necessary. Move the taking of the mutex later. This avoids
holding it unnecessarily across the vmalloc() and copy_from_user()
of the policy data.

Cc: stable@vger.kernel.org
Signed-off-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: stephensmalley

security/selinux/selinuxfs.c

@@ -594,34 +594,31 @@ static ssize_t sel_write_load(struct file *file, const char __user *buf,
 	if (!count)
 		return -EINVAL;
 
-	mutex_lock(&selinux_state.policy_mutex);
-
 	length = avc_has_perm(current_sid(), SECINITSID_SECURITY,
 			      SECCLASS_SECURITY, SECURITY__LOAD_POLICY, NULL);
 	if (length)
-		goto out;
+		return length;
 
 	data = vmalloc(count);
-	if (!data) {
-		length = -ENOMEM;
-		goto out;
-	}
+	if (!data)
+		return -ENOMEM;
 	if (copy_from_user(data, buf, count) != 0) {
 		length = -EFAULT;
 		goto out;
 	}
 
+	mutex_lock(&selinux_state.policy_mutex);
 	length = security_load_policy(data, count, &load_state);
 	if (length) {
 		pr_warn_ratelimited("SELinux: failed to load policy\n");
-		goto out;
+		goto out_unlock;
 	}
 	fsi = file_inode(file)->i_sb->s_fs_info;
 	length = sel_make_policy_nodes(fsi, load_state.policy);
 	if (length) {
 		pr_warn_ratelimited("SELinux: failed to initialize selinuxfs\n");
 		selinux_policy_cancel(&load_state);
-		goto out;
+		goto out_unlock;
 	}
 
 	selinux_policy_commit(&load_state);
@@ -631,8 +628,9 @@ static ssize_t sel_write_load(struct file *file, const char __user *buf,
 		from_kuid(&init_user_ns, audit_get_loginuid(current)),
 		audit_get_sessionid(current));
 
-out:
+out_unlock:
 	mutex_unlock(&selinux_state.policy_mutex);
+out:
 	vfree(data);
 	return length;
 }