Code: static ssize_t o2nm_node_num_store(struct config_item *item, const char *page,
 				   size_t count)
 {
 	struct o2nm_node *node = to_o2nm_node(item);
	struct o2nm_cluster *cluster = to_o2nm_cluster_from_node(node);
 	unsigned long tmp;
 	char *p = (char *)page;
 	int ret = 0;

	tmp = simple_strtoul(p, &p, 0);
	if (!p || (*p && (*p != '\n')))
		return -EINVAL;

	if (tmp >= O2NM_MAX_NODES)
		return -ERANGE;

	/* once we're in the cl_nodes tree networking can look us up by
	 * node number and try to use our address and port attributes
	 * to connect to this node.. make sure that they've been set
	 * before writing the node attribute? */
	if (!test_bit(O2NM_NODE_ATTR_ADDRESS, &node->nd_set_attributes) ||
 	    !test_bit(O2NM_NODE_ATTR_PORT, &node->nd_set_attributes))
 		return -EINVAL; /* XXX */
 
 	write_lock(&cluster->cl_nodes_lock);
 	if (cluster->cl_nodes[tmp])
 		ret = -EEXIST;
	else if (test_and_set_bit(O2NM_NODE_ATTR_NUM,
			&node->nd_set_attributes))
		ret = -EBUSY;
	else  {
		cluster->cl_nodes[tmp] = node;
		node->nd_num = tmp;
 		set_bit(tmp, cluster->cl_nodes_bitmap);
 	}
 	write_unlock(&cluster->cl_nodes_lock);
 	if (ret)
 		return ret;
 
	return count;
}

Vulnerability Type: DoS 
CWE ID: CWE-476
Summary: In fs/ocfs2/cluster/nodemanager.c in the Linux kernel before 4.15, local users can cause a denial of service (NULL pointer dereference and BUG) because a required mutex is not used.
Commit Message: ocfs2: subsystem.su_mutex is required while accessing the item->ci_parent

The subsystem.su_mutex is required while accessing the item->ci_parent,
otherwise, NULL pointer dereference to the item->ci_parent will be
triggered in the following situation:

add node                     delete node
sys_write
 vfs_write
  configfs_write_file
   o2nm_node_store
    o2nm_node_local_write
                             do_rmdir
                              vfs_rmdir
                               configfs_rmdir
                                mutex_lock(&subsys->su_mutex);
                                unlink_obj
                                 item->ci_group = NULL;
                                 item->ci_parent = NULL;
	 to_o2nm_cluster_from_node
	  node->nd_item.ci_parent->ci_parent
	  BUG since of NULL pointer dereference to nd_item.ci_parent

Moreover, the o2nm_cluster also should be protected by the
subsystem.su_mutex.

[alex.chen@huawei.com: v2]
  Link: http://lkml.kernel.org/r/59EEAA69.9080703@huawei.com
Link: http://lkml.kernel.org/r/59E9B36A.10700@huawei.com
Signed-off-by: Alex Chen <alex.chen@huawei.com>
Reviewed-by: Jun Piao <piaojun@huawei.com>
Reviewed-by: Joseph Qi <jiangqi903@gmail.com>
Cc: Mark Fasheh <mfasheh@versity.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>