tipc: fix race in disc create/delete

Commit a21a584d67 (tipc: fix neighbor
detection problem after hw address change) introduces a race condition
involving tipc_disc_delete() and tipc_disc_add/remove_dest that can
cause TIPC to dereference the pointer to the bearer discovery request
structure after it has been freed since a stray pointer is left in the
bearer structure.

In order to fix the issue, the process of resetting the discovery
request handler is optimized: the discovery request handler and request
buffer are just reset instead of being freed, allocated and initialized.
As the request point is always valid and the request's lock is taken
while the request handler is reset, the race doesn't happen any more.

Reported-by: Erik Hugne <erik.hugne@ericsson.com>
Signed-off-by: Ying Xue <ying.xue@windriver.com>
Reviewed-by: Erik Hugne <erik.hugne@ericsson.com>
Tested-by: Erik Hugne <erik.hugne@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/bearer.c

@@ -365,9 +365,8 @@ restart:
 static int tipc_reset_bearer(struct tipc_bearer *b_ptr)
 {
 	pr_info("Resetting bearer <%s>\n", b_ptr->name);
-	tipc_disc_delete(b_ptr->link_req);
 	tipc_link_reset_list(b_ptr->identity);
-	tipc_disc_create(b_ptr, &b_ptr->bcast_addr);
+	tipc_disc_reset(b_ptr);
 	return 0;
 }
 

net/tipc/discover.c

@@ -71,22 +71,19 @@ struct tipc_link_req {
  * @type: message type (request or response)
  * @b_ptr: ptr to bearer issuing message
  */
-static struct sk_buff *tipc_disc_init_msg(u32 type, struct tipc_bearer *b_ptr)
+static void tipc_disc_init_msg(struct sk_buff *buf, u32 type,
+			       struct tipc_bearer *b_ptr)
 {
-	struct sk_buff *buf = tipc_buf_acquire(INT_H_SIZE);
 	struct tipc_msg *msg;
 	u32 dest_domain = b_ptr->domain;
 
-	if (buf) {
-		msg = buf_msg(buf);
-		tipc_msg_init(msg, LINK_CONFIG, type, INT_H_SIZE, dest_domain);
-		msg_set_non_seq(msg, 1);
-		msg_set_node_sig(msg, tipc_random);
-		msg_set_dest_domain(msg, dest_domain);
-		msg_set_bc_netid(msg, tipc_net_id);
-		b_ptr->media->addr2msg(&b_ptr->addr, msg_media_addr(msg));
-	}
-	return buf;
+	msg = buf_msg(buf);
+	tipc_msg_init(msg, LINK_CONFIG, type, INT_H_SIZE, dest_domain);
+	msg_set_non_seq(msg, 1);
+	msg_set_node_sig(msg, tipc_random);
+	msg_set_dest_domain(msg, dest_domain);
+	msg_set_bc_netid(msg, tipc_net_id);
+	b_ptr->media->addr2msg(&b_ptr->addr, msg_media_addr(msg));
 }
 
 /**
@@ -241,8 +238,9 @@ void tipc_disc_rcv(struct sk_buff *buf, struct tipc_bearer *b_ptr)
 	link_fully_up = link_working_working(link);
 
 	if ((type == DSC_REQ_MSG) && !link_fully_up) {
-		rbuf = tipc_disc_init_msg(DSC_RESP_MSG, b_ptr);
+		rbuf = tipc_buf_acquire(INT_H_SIZE);
 		if (rbuf) {
+			tipc_disc_init_msg(rbuf, DSC_RESP_MSG, b_ptr);
 			tipc_bearer_send(b_ptr->identity, rbuf, &media_addr);
 			kfree_skb(rbuf);
 		}
@@ -349,12 +347,11 @@ int tipc_disc_create(struct tipc_bearer *b_ptr, struct tipc_media_addr *dest)
 	if (!req)
 		return -ENOMEM;
 
-	req->buf = tipc_disc_init_msg(DSC_REQ_MSG, b_ptr);
-	if (!req->buf) {
-		kfree(req);
-		return -ENOMSG;
-	}
+	req->buf = tipc_buf_acquire(INT_H_SIZE);
+	if (!req->buf)
+		return -ENOMEM;
 
+	tipc_disc_init_msg(req->buf, DSC_REQ_MSG, b_ptr);
 	memcpy(&req->dest, dest, sizeof(*dest));
 	req->bearer_id = b_ptr->identity;
 	req->domain = b_ptr->domain;
@@ -379,3 +376,23 @@ void tipc_disc_delete(struct tipc_link_req *req)
 	kfree_skb(req->buf);
 	kfree(req);
 }
+
+/**
+ * tipc_disc_reset - reset object to send periodic link setup requests
+ * @b_ptr: ptr to bearer issuing requests
+ * @dest_domain: network domain to which links can be established
+ */
+void tipc_disc_reset(struct tipc_bearer *b_ptr)
+{
+	struct tipc_link_req *req = b_ptr->link_req;
+
+	spin_lock_bh(&req->lock);
+	tipc_disc_init_msg(req->buf, DSC_REQ_MSG, b_ptr);
+	req->bearer_id = b_ptr->identity;
+	req->domain = b_ptr->domain;
+	req->num_nodes = 0;
+	req->timer_intv = TIPC_LINK_REQ_INIT;
+	k_start_timer(&req->timer, req->timer_intv);
+	tipc_bearer_send(req->bearer_id, req->buf, &req->dest);
+	spin_unlock_bh(&req->lock);
+}

net/tipc/discover.h

@@ -41,6 +41,7 @@ struct tipc_link_req;
 
 int tipc_disc_create(struct tipc_bearer *b_ptr, struct tipc_media_addr *dest);
 void tipc_disc_delete(struct tipc_link_req *req);
+void tipc_disc_reset(struct tipc_bearer *b_ptr);
 void tipc_disc_add_dest(struct tipc_link_req *req);
 void tipc_disc_remove_dest(struct tipc_link_req *req);
 void tipc_disc_rcv(struct sk_buff *buf, struct tipc_bearer *b_ptr);