Patch "xenbus: don't BUG() on user mode induced condition" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
xenbus-don-t-bug-on-user-mode-induced-condition.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jan Beulich <[email protected]>
Date: Thu, 7 Jul 2016 01:23:57 -0600
Subject: xenbus: don't BUG() on user mode induced condition

From: Jan Beulich <[email protected]>

commit 0beef634b86a1350c31da5fcc2992f0d7c8a622b upstream.

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.

---
 drivers/xen/xenbus/xenbus_dev_frontend.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

@@ -316,11 +316,18 @@ static int xenbus_write_transaction(unsi
 			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(unsi
 			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);
 	}
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/xen-pciback-fix-conf_space-read-write-overlap-check.patch queue-4.4/xenbus-don-t-bail-early-from-xenbus_dev_request_and_reply.patch queue-4.4/xenbus-don-t-bug-on-user-mode-induced-condition.patch