drbd: Fix five use after free bugs in get_initial_state

In get_initial_state, it calls notify_initial_state_done(skb,..) if
cb->args[5]==1. If genlmsg_put() failed in notify_initial_state_done(),
the skb will be freed by nlmsg_free(skb).
Then get_initial_state will goto out and the freed skb will be used by
return value skb->len, which is a uaf bug.

What's worse, the same problem goes even further: skb can also be
freed in the notify_*_state_change -> notify_*_state calls below.
Thus 4 additional uaf bugs happened.

My patch lets the problem callee functions: notify_initial_state_done
and notify_*_state_change return an error code if errors happen.
So that the error codes could be propagated and the uaf bugs can be avoid.

v2 reports a compilation warning. This v3 fixed this warning and built
successfully in my local environment with no additional warnings.
v2: https://lore.kernel.org/patchwork/patch/1435218/

Fixes: a29728463b254 ("drbd: Backport the "events2" command")
Signed-off-by: Lv Yunlong <[e-mail]>
Reviewed-by: Christoph Böhmwalder <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/block/drbd/drbd_int.h

···
 };
 void drbd_bcast_event(struct drbd_device *device, const struct sib_info *sib);
 
-extern void notify_resource_state(struct sk_buff *,
+extern int notify_resource_state(struct sk_buff *,
 				  unsigned int,
 				  struct drbd_resource *,
 				  struct resource_info *,
 				  enum drbd_notification_type);
-extern void notify_device_state(struct sk_buff *,
+extern int notify_device_state(struct sk_buff *,
 				unsigned int,
 				struct drbd_device *,
 				struct device_info *,
 				enum drbd_notification_type);
-extern void notify_connection_state(struct sk_buff *,
+extern int notify_connection_state(struct sk_buff *,
 				    unsigned int,
 				    struct drbd_connection *,
 				    struct connection_info *,
 				    enum drbd_notification_type);
-extern void notify_peer_device_state(struct sk_buff *,
+extern int notify_peer_device_state(struct sk_buff *,
 				     unsigned int,
 				     struct drbd_peer_device *,
 				     struct peer_device_info *,

drivers/block/drbd/drbd_nl.c

···
 	return drbd_notification_header_to_skb(msg, &nh, true);
 }
 
-void notify_resource_state(struct sk_buff *skb,
+int notify_resource_state(struct sk_buff *skb,
 			   unsigned int seq,
 			   struct drbd_resource *resource,
 			   struct resource_info *resource_info,
···
 		if (err && err != -ESRCH)
 			goto failed;
 	}
-	return;
+	return 0;
 
 nla_put_failure:
 	nlmsg_free(skb);
 failed:
 	drbd_err(resource, "Error %d while broadcasting event. Event seq:%u\n",
 			err, seq);
+	return err;
 }
 
-void notify_device_state(struct sk_buff *skb,
+int notify_device_state(struct sk_buff *skb,
 			 unsigned int seq,
 			 struct drbd_device *device,
 			 struct device_info *device_info,
···
 		if (err && err != -ESRCH)
 			goto failed;
 	}
-	return;
+	return 0;
 
 nla_put_failure:
 	nlmsg_free(skb);
 failed:
 	drbd_err(device, "Error %d while broadcasting event. Event seq:%u\n",
 		 err, seq);
+	return err;
 }
 
-void notify_connection_state(struct sk_buff *skb,
+int notify_connection_state(struct sk_buff *skb,
 			     unsigned int seq,
 			     struct drbd_connection *connection,
 			     struct connection_info *connection_info,
···
 		if (err && err != -ESRCH)
 			goto failed;
 	}
-	return;
+	return 0;
 
 nla_put_failure:
 	nlmsg_free(skb);
 failed:
 	drbd_err(connection, "Error %d while broadcasting event. Event seq:%u\n",
 		 err, seq);
+	return err;
 }
 
-void notify_peer_device_state(struct sk_buff *skb,
+int notify_peer_device_state(struct sk_buff *skb,
 			      unsigned int seq,
 			      struct drbd_peer_device *peer_device,
 			      struct peer_device_info *peer_device_info,
···
 		if (err && err != -ESRCH)
 			goto failed;
 	}
-	return;
+	return 0;
 
 nla_put_failure:
 	nlmsg_free(skb);
 failed:
 	drbd_err(peer_device, "Error %d while broadcasting event. Event seq:%u\n",
 		 err, seq);
+	return err;
 }
 
 void notify_helper(enum drbd_notification_type type,
···
 		 err, seq);
 }
 
-static void notify_initial_state_done(struct sk_buff *skb, unsigned int seq)
+static int notify_initial_state_done(struct sk_buff *skb, unsigned int seq)
 {
 	struct drbd_genlmsghdr *dh;
 	int err;
···
 	if (nla_put_notification_header(skb, NOTIFY_EXISTS))
 		goto nla_put_failure;
 	genlmsg_end(skb, dh);
-	return;
+	return 0;
 
 nla_put_failure:
 	nlmsg_free(skb);
 	pr_err("Error %d sending event. Event seq:%u\n", err, seq);
+	return err;
 }
 
 static void free_state_changes(struct list_head *list)
···
 	unsigned int seq = cb->args[2];
 	unsigned int n;
 	enum drbd_notification_type flags = 0;
+	int err = 0;
 
 	/* There is no need for taking notification_mutex here: it doesn't
 	   matter if the initial state events mix with later state chage
···
 
 	cb->args[5]--;
 	if (cb->args[5] == 1) {
-		notify_initial_state_done(skb, seq);
+		err = notify_initial_state_done(skb, seq);
 		goto out;
 	}
 	n = cb->args[4]++;
 	if (cb->args[4] < cb->args[3])
 		flags |= NOTIFY_CONTINUES;
 	if (n < 1) {
-		notify_resource_state_change(skb, seq, state_change->resource,
+		err = notify_resource_state_change(skb, seq, state_change->resource,
 					     NOTIFY_EXISTS | flags);
 		goto next;
 	}
 	n--;
 	if (n < state_change->n_connections) {
-		notify_connection_state_change(skb, seq, &state_change->connections[n],
+		err = notify_connection_state_change(skb, seq, &state_change->connections[n],
 					       NOTIFY_EXISTS | flags);
 		goto next;
 	}
 	n -= state_change->n_connections;
 	if (n < state_change->n_devices) {
-		notify_device_state_change(skb, seq, &state_change->devices[n],
+		err = notify_device_state_change(skb, seq, &state_change->devices[n],
 					   NOTIFY_EXISTS | flags);
 		goto next;
 	}
 	n -= state_change->n_devices;
 	if (n < state_change->n_devices * state_change->n_connections) {
-		notify_peer_device_state_change(skb, seq, &state_change->peer_devices[n],
+		err = notify_peer_device_state_change(skb, seq, &state_change->peer_devices[n],
 						NOTIFY_EXISTS | flags);
 		goto next;
 	}
···
 		cb->args[4] = 0;
 	}
 out:
-	return skb->len;
+	if (err)
+		return err;
+	else
+		return skb->len;
 }
 
 int drbd_adm_get_initial_state(struct sk_buff *skb, struct netlink_callback *cb)

drivers/block/drbd/drbd_state.c

···
 	return rv;
 }
 
-void notify_resource_state_change(struct sk_buff *skb,
+int notify_resource_state_change(struct sk_buff *skb,
 				  unsigned int seq,
 				  struct drbd_resource_state_change *resource_state_change,
 				  enum drbd_notification_type type)
···
 		.res_susp_fen = resource_state_change->susp_fen[NEW],
 	};
 
-	notify_resource_state(skb, seq, resource, &resource_info, type);
+	return notify_resource_state(skb, seq, resource, &resource_info, type);
 }
 
-void notify_connection_state_change(struct sk_buff *skb,
+int notify_connection_state_change(struct sk_buff *skb,
 				    unsigned int seq,
 				    struct drbd_connection_state_change *connection_state_change,
 				    enum drbd_notification_type type)
···
 		.conn_role = connection_state_change->peer_role[NEW],
 	};
 
-	notify_connection_state(skb, seq, connection, &connection_info, type);
+	return notify_connection_state(skb, seq, connection, &connection_info, type);
 }
 
-void notify_device_state_change(struct sk_buff *skb,
+int notify_device_state_change(struct sk_buff *skb,
 				unsigned int seq,
 				struct drbd_device_state_change *device_state_change,
 				enum drbd_notification_type type)
···
 		.dev_disk_state = device_state_change->disk_state[NEW],
 	};
 
-	notify_device_state(skb, seq, device, &device_info, type);
+	return notify_device_state(skb, seq, device, &device_info, type);
 }
 
-void notify_peer_device_state_change(struct sk_buff *skb,
+int notify_peer_device_state_change(struct sk_buff *skb,
 				     unsigned int seq,
 				     struct drbd_peer_device_state_change *p,
 				     enum drbd_notification_type type)
···
 		.peer_resync_susp_dependency = p->resync_susp_dependency[NEW],
 	};
 
-	notify_peer_device_state(skb, seq, peer_device, &peer_device_info, type);
+	return notify_peer_device_state(skb, seq, peer_device, &peer_device_info, type);
 }
 
 static void broadcast_state_change(struct drbd_state_change *state_change)
···
 	struct drbd_resource_state_change *resource_state_change = &state_change->resource[0];
 	bool resource_state_has_changed;
 	unsigned int n_device, n_connection, n_peer_device, n_peer_devices;
-	void (*last_func)(struct sk_buff *, unsigned int, void *,
+	int (*last_func)(struct sk_buff *, unsigned int, void *,
 			  enum drbd_notification_type) = NULL;
 	void *last_arg = NULL;
 

drivers/block/drbd/drbd_state_change.h

···
 extern void copy_old_to_new_state_change(struct drbd_state_change *);
 extern void forget_state_change(struct drbd_state_change *);
 
-extern void notify_resource_state_change(struct sk_buff *,
+extern int notify_resource_state_change(struct sk_buff *,
 					 unsigned int,
 					 struct drbd_resource_state_change *,
 					 enum drbd_notification_type type);
-extern void notify_connection_state_change(struct sk_buff *,
+extern int notify_connection_state_change(struct sk_buff *,
 					   unsigned int,
 					   struct drbd_connection_state_change *,
 					   enum drbd_notification_type type);
-extern void notify_device_state_change(struct sk_buff *,
+extern int notify_device_state_change(struct sk_buff *,
 				       unsigned int,
 				       struct drbd_device_state_change *,
 				       enum drbd_notification_type type);
-extern void notify_peer_device_state_change(struct sk_buff *,
+extern int notify_peer_device_state_change(struct sk_buff *,
 					    unsigned int,
 					    struct drbd_peer_device_state_change *,
 					    enum drbd_notification_type type);