Vulnerability: 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.
Vulnerability ID: CVE-2017-18216
CWE: CWE-476
Severity score: 2.9
Project: https://github.com/torvalds/linux
Published: 2018-03-05
File: fs/ocfs2/cluster/nodemanager.c
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>
Commit author: alex chen

Vulnerable version (before fix):
 char *o2nm_fence_method_desc[O2NM_FENCE_METHODS] = { 		"panic",	/* O2NM_FENCE_PANIC */ };  struct o2nm_node *o2nm_get_node_by_num(u8 node_num) { 	struct o2nm_node *node = NULL; static struct o2nm_cluster *to_o2nm_cluster_from_node(struct o2nm_node *node) { 	/* through the first node_set .parent 	 * mycluster/nodes/mynode == o2nm_cluster->o2nm_node_group->o2nm_node */ 	return to_o2nm_cluster(node->nd_item.ci_parent->ci_parent); }  enum { 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; static ssize_t o2nm_node_num_store(struct config_item *item, const char *page, 	    !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; static ssize_t o2nm_node_num_store(struct config_item *item, const char *page, 		set_bit(tmp, cluster->cl_nodes_bitmap); 	} 	write_unlock(&cluster->cl_nodes_lock); 	if (ret) 		return ret;  static ssize_t o2nm_node_ipv4_address_store(struct config_item *item, 					    size_t count) { 	struct o2nm_node *node = to_o2nm_node(item); 	struct o2nm_cluster *cluster = to_o2nm_cluster_from_node(node); 	int ret, i; 	struct rb_node **p, *parent; 	unsigned int octets[4]; static ssize_t o2nm_node_ipv4_address_store(struct config_item *item, 		be32_add_cpu(&ipv4_addr, octets[i] << (i * 8)); 	}  	ret = 0; 	write_lock(&cluster->cl_nodes_lock); 	if (o2nm_node_ip_tree_lookup(cluster, ipv4_addr, &p, &parent)) static ssize_t o2nm_node_ipv4_address_store(struct config_item *item, 		rb_insert_color(&node->nd_ip_node, &cluster->cl_node_ip_tree); 	} 	write_unlock(&cluster->cl_nodes_lock); 	if (ret) 		return ret;  static ssize_t o2nm_node_local_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; 	ssize_t ret; static ssize_t o2nm_node_local_store(struct config_item *item, const char *page, 	    !test_bit(O2NM_NODE_ATTR_PORT, &node->nd_set_attributes)) 		return -EINVAL; /* XXX */  	/* the only failure case is trying to set a new local node 	 * when a different one is already set */ 	if (tmp && tmp == cluster->cl_has_local && 	    cluster->cl_local_node != node->nd_num) 		return -EBUSY;  	/* bring up the rx thread if we're setting the new local node. */ 	if (tmp && !cluster->cl_has_local) { 		ret = o2net_start_listening(node); 		if (ret) 			return ret; 	}  	if (!tmp && cluster->cl_has_local && static ssize_t o2nm_node_local_store(struct config_item *item, const char *page, 		cluster->cl_local_node = node->nd_num; 	}  	return count; }  CONFIGFS_ATTR(o2nm_node_, num); static struct o2nm_cluster_group o2nm_cluster_group = { 	}, };  int o2nm_depend_item(struct config_item *item) { 	return configfs_depend_item(&o2nm_cluster_group.cs_subsys, item);

Fixed version (after fix):
 char *o2nm_fence_method_desc[O2NM_FENCE_METHODS] = { 		"panic",	/* O2NM_FENCE_PANIC */ };  static inline void o2nm_lock_subsystem(void); static inline void o2nm_unlock_subsystem(void);  struct o2nm_node *o2nm_get_node_by_num(u8 node_num) { 	struct o2nm_node *node = NULL; static struct o2nm_cluster *to_o2nm_cluster_from_node(struct o2nm_node *node) { 	/* through the first node_set .parent 	 * mycluster/nodes/mynode == o2nm_cluster->o2nm_node_group->o2nm_node */ 	if (node->nd_item.ci_parent) 		return to_o2nm_cluster(node->nd_item.ci_parent->ci_parent); 	else 		return NULL; }  enum { 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; 	unsigned long tmp; 	char *p = (char *)page; 	int ret = 0; static ssize_t o2nm_node_num_store(struct config_item *item, const char *page, 	    !test_bit(O2NM_NODE_ATTR_PORT, &node->nd_set_attributes)) 		return -EINVAL; /* XXX */  	o2nm_lock_subsystem(); 	cluster = to_o2nm_cluster_from_node(node); 	if (!cluster) { 		o2nm_unlock_subsystem(); 		return -EINVAL; 	}  	write_lock(&cluster->cl_nodes_lock); 	if (cluster->cl_nodes[tmp]) 		ret = -EEXIST; static ssize_t o2nm_node_num_store(struct config_item *item, const char *page, 		set_bit(tmp, cluster->cl_nodes_bitmap); 	} 	write_unlock(&cluster->cl_nodes_lock); 	o2nm_unlock_subsystem();  	if (ret) 		return ret;  static ssize_t o2nm_node_ipv4_address_store(struct config_item *item, 					    size_t count) { 	struct o2nm_node *node = to_o2nm_node(item); 	struct o2nm_cluster *cluster; 	int ret, i; 	struct rb_node **p, *parent; 	unsigned int octets[4]; static ssize_t o2nm_node_ipv4_address_store(struct config_item *item, 		be32_add_cpu(&ipv4_addr, octets[i] << (i * 8)); 	}  	o2nm_lock_subsystem(); 	cluster = to_o2nm_cluster_from_node(node); 	if (!cluster) { 		o2nm_unlock_subsystem(); 		return -EINVAL; 	}  	ret = 0; 	write_lock(&cluster->cl_nodes_lock); 	if (o2nm_node_ip_tree_lookup(cluster, ipv4_addr, &p, &parent)) static ssize_t o2nm_node_ipv4_address_store(struct config_item *item, 		rb_insert_color(&node->nd_ip_node, &cluster->cl_node_ip_tree); 	} 	write_unlock(&cluster->cl_nodes_lock); 	o2nm_unlock_subsystem();  	if (ret) 		return ret;  static ssize_t o2nm_node_local_store(struct config_item *item, const char *page, 				     size_t count) { 	struct o2nm_node *node = to_o2nm_node(item); 	struct o2nm_cluster *cluster; 	unsigned long tmp; 	char *p = (char *)page; 	ssize_t ret; static ssize_t o2nm_node_local_store(struct config_item *item, const char *page, 	    !test_bit(O2NM_NODE_ATTR_PORT, &node->nd_set_attributes)) 		return -EINVAL; /* XXX */  	o2nm_lock_subsystem(); 	cluster = to_o2nm_cluster_from_node(node); 	if (!cluster) { 		ret = -EINVAL; 		goto out; 	}  	/* the only failure case is trying to set a new local node 	 * when a different one is already set */ 	if (tmp && tmp == cluster->cl_has_local && 	    cluster->cl_local_node != node->nd_num) { 		ret = -EBUSY; 		goto out; 	}  	/* bring up the rx thread if we're setting the new local node. */ 	if (tmp && !cluster->cl_has_local) { 		ret = o2net_start_listening(node); 		if (ret) 			goto out; 	}  	if (!tmp && cluster->cl_has_local && static ssize_t o2nm_node_local_store(struct config_item *item, const char *page, 		cluster->cl_local_node = node->nd_num; 	}  	ret = count;  out: 	o2nm_unlock_subsystem(); 	return ret; }  CONFIGFS_ATTR(o2nm_node_, num); static struct o2nm_cluster_group o2nm_cluster_group = { 	}, };  static inline void o2nm_lock_subsystem(void) { 	mutex_lock(&o2nm_cluster_group.cs_subsys.su_mutex); }  static inline void o2nm_unlock_subsystem(void) { 	mutex_unlock(&o2nm_cluster_group.cs_subsys.su_mutex); }  int o2nm_depend_item(struct config_item *item) { 	return configfs_depend_item(&o2nm_cluster_group.cs_subsys, item);

Patch:
patch: @@ -40,6 +40,9 @@ char *o2nm_fence_method_desc[O2NM_FENCE_METHODS] = {
 		"panic",	/* O2NM_FENCE_PANIC */
 };
 
+static inline void o2nm_lock_subsystem(void);
+static inline void o2nm_unlock_subsystem(void);
+
 struct o2nm_node *o2nm_get_node_by_num(u8 node_num)
 {
 	struct o2nm_node *node = NULL;
@@ -181,7 +184,10 @@ static struct o2nm_cluster *to_o2nm_cluster_from_node(struct o2nm_node *node)
 {
 	/* through the first node_set .parent
 	 * mycluster/nodes/mynode == o2nm_cluster->o2nm_node_group->o2nm_node */
-	return to_o2nm_cluster(node->nd_item.ci_parent->ci_parent);
+	if (node->nd_item.ci_parent)
+		return to_o2nm_cluster(node->nd_item.ci_parent->ci_parent);
+	else
+		return NULL;
 }
 
 enum {
@@ -194,7 +200,7 @@ 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);
+	struct o2nm_cluster *cluster;
 	unsigned long tmp;
 	char *p = (char *)page;
 	int ret = 0;
@@ -214,6 +220,13 @@ static ssize_t o2nm_node_num_store(struct config_item *item, const char *page,
 	    !test_bit(O2NM_NODE_ATTR_PORT, &node->nd_set_attributes))
 		return -EINVAL; /* XXX */
 
+	o2nm_lock_subsystem();
+	cluster = to_o2nm_cluster_from_node(node);
+	if (!cluster) {
+		o2nm_unlock_subsystem();
+		return -EINVAL;
+	}
+
 	write_lock(&cluster->cl_nodes_lock);
 	if (cluster->cl_nodes[tmp])
 		ret = -EEXIST;
@@ -226,6 +239,8 @@ static ssize_t o2nm_node_num_store(struct config_item *item, const char *page,
 		set_bit(tmp, cluster->cl_nodes_bitmap);
 	}
 	write_unlock(&cluster->cl_nodes_lock);
+	o2nm_unlock_subsystem();
+
 	if (ret)
 		return ret;
 
@@ -269,7 +284,7 @@ static ssize_t o2nm_node_ipv4_address_store(struct config_item *item,
 					    size_t count)
 {
 	struct o2nm_node *node = to_o2nm_node(item);
-	struct o2nm_cluster *cluster = to_o2nm_cluster_from_node(node);
+	struct o2nm_cluster *cluster;
 	int ret, i;
 	struct rb_node **p, *parent;
 	unsigned int octets[4];
@@ -286,6 +301,13 @@ static ssize_t o2nm_node_ipv4_address_store(struct config_item *item,
 		be32_add_cpu(&ipv4_addr, octets[i] << (i * 8));
 	}
 
+	o2nm_lock_subsystem();
+	cluster = to_o2nm_cluster_from_node(node);
+	if (!cluster) {
+		o2nm_unlock_subsystem();
+		return -EINVAL;
+	}
+
 	ret = 0;
 	write_lock(&cluster->cl_nodes_lock);
 	if (o2nm_node_ip_tree_lookup(cluster, ipv4_addr, &p, &parent))
@@ -298,6 +320,8 @@ static ssize_t o2nm_node_ipv4_address_store(struct config_item *item,
 		rb_insert_color(&node->nd_ip_node, &cluster->cl_node_ip_tree);
 	}
 	write_unlock(&cluster->cl_nodes_lock);
+	o2nm_unlock_subsystem();
+
 	if (ret)
 		return ret;
 
@@ -315,7 +339,7 @@ static ssize_t o2nm_node_local_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);
+	struct o2nm_cluster *cluster;
 	unsigned long tmp;
 	char *p = (char *)page;
 	ssize_t ret;
@@ -333,17 +357,26 @@ static ssize_t o2nm_node_local_store(struct config_item *item, const char *page,
 	    !test_bit(O2NM_NODE_ATTR_PORT, &node->nd_set_attributes))
 		return -EINVAL; /* XXX */
 
+	o2nm_lock_subsystem();
+	cluster = to_o2nm_cluster_from_node(node);
+	if (!cluster) {
+		ret = -EINVAL;
+		goto out;
+	}
+
 	/* the only failure case is trying to set a new local node
 	 * when a different one is already set */
 	if (tmp && tmp == cluster->cl_has_local &&
-	    cluster->cl_local_node != node->nd_num)
-		return -EBUSY;
+	    cluster->cl_local_node != node->nd_num) {
+		ret = -EBUSY;
+		goto out;
+	}
 
 	/* bring up the rx thread if we're setting the new local node. */
 	if (tmp && !cluster->cl_has_local) {
 		ret = o2net_start_listening(node);
 		if (ret)
-			return ret;
+			goto out;
 	}
 
 	if (!tmp && cluster->cl_has_local &&
@@ -358,7 +391,11 @@ static ssize_t o2nm_node_local_store(struct config_item *item, const char *page,
 		cluster->cl_local_node = node->nd_num;
 	}
 
-	return count;
+	ret = count;
+
+out:
+	o2nm_unlock_subsystem();
+	return ret;
 }
 
 CONFIGFS_ATTR(o2nm_node_, num);
@@ -738,6 +775,16 @@ static struct o2nm_cluster_group o2nm_cluster_group = {
 	},
 };
 
+static inline void o2nm_lock_subsystem(void)
+{
+	mutex_lock(&o2nm_cluster_group.cs_subsys.su_mutex);
+}
+
+static inline void o2nm_unlock_subsystem(void)
+{
+	mutex_unlock(&o2nm_cluster_group.cs_subsys.su_mutex);
+}
+
 int o2nm_depend_item(struct config_item *item)
 {
 	return configfs_depend_item(&o2nm_cluster_group.cs_subsys, item);
path: fs/ocfs2/cluster/nodemanager.c