xenbus: don't BUG() on user mode induced condition

Inability to locate a user mode specified transaction ID should not
lead to a kernel crash. For other than XS_TRANSACTION_START also
don't issue anything to xenbus if the specified ID doesn't match that
of any active transaction.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

diff --git a/drivers/xen/xenbus/xenbus_dev_frontend.c b/drivers/xen/xenbus/xenbus_dev_frontend.c
index cacf30d14747baa20d5f2d8a6a999ebdcba14018..7487971f9f788b12a637216c29cc853bb933c1ca 100644 (file)
--- a/drivers/xen/xenbus/xenbus_dev_frontend.c
+++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
@@ -316,11 +316,18 @@ static int xenbus_write_transaction(unsigned msg_type,
                        rc = -ENOMEM;
                        goto out;
                }
+       } else {
+               list_for_each_entry(trans, &u->transactions, list)
+                       if (trans->handle.id == u->u.msg.tx_id)
+                               break;
+               if (&trans->list == &u->transactions)
+                       return -ESRCH;
        }
 
        reply = xenbus_dev_request_and_reply(&u->u.msg);
        if (IS_ERR(reply)) {
-               kfree(trans);
+               if (msg_type == XS_TRANSACTION_START)
+                       kfree(trans);
                rc = PTR_ERR(reply);
                goto out;
        }
@@ -333,12 +340,7 @@ static int xenbus_write_transaction(unsigned msg_type,
                        list_add(&trans->list, &u->transactions);
                }
        } else if (u->u.msg.type == XS_TRANSACTION_END) {
-               list_for_each_entry(trans, &u->transactions, list)
-                       if (trans->handle.id == u->u.msg.tx_id)
-                               break;
-               BUG_ON(&trans->list == &u->transactions);
                list_del(&trans->list);
-
                kfree(trans);
        }