Patch "xen/xenbus: reference count registered modules" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    xen/xenbus: reference count registered modules

to the 5.4-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:
     xen-xenbus-reference-count-registered-modules.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 7bd8b2a692c2f6799ae7a98e0ccbb48eaf433922
Author: Paul Durrant <pdurrant@xxxxxxxxxx>
Date:   Mon Dec 2 11:41:16 2019 +0000

    xen/xenbus: reference count registered modules
    
    [ Upstream commit 196748a276b4dee01177e6b7abcda27cd759de83 ]
    
    To prevent a PV driver module being removed whilst attached to its other
    end, and hence xenbus calling into potentially invalid text, take a
    reference on the module before calling the probe() method (dropping it if
    unsuccessful) and drop the reference after returning from the remove()
    method.
    
    Suggested-by: Jan Beulich <jbeulich@xxxxxxxx>
    Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Stable-dep-of: afc545da381b ("xen: Fix the issue of resource not being properly released in xenbus_dev_probe()")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index b911a91bce6b7..9215099caad61 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -233,9 +233,16 @@ int xenbus_dev_probe(struct device *_dev)
 		return err;
 	}
 
+	if (!try_module_get(drv->driver.owner)) {
+		dev_warn(&dev->dev, "failed to acquire module reference on '%s'\n",
+			 drv->driver.name);
+		err = -ESRCH;
+		goto fail;
+	}
+
 	err = drv->probe(dev, id);
 	if (err)
-		goto fail;
+		goto fail_put;
 
 	err = watch_otherend(dev);
 	if (err) {
@@ -245,6 +252,8 @@ int xenbus_dev_probe(struct device *_dev)
 	}
 
 	return 0;
+fail_put:
+	module_put(drv->driver.owner);
 fail:
 	xenbus_dev_error(dev, err, "xenbus_dev_probe on %s", dev->nodename);
 	xenbus_switch_state(dev, XenbusStateClosed);
@@ -264,6 +273,8 @@ int xenbus_dev_remove(struct device *_dev)
 	if (drv->remove)
 		drv->remove(dev);
 
+	module_put(drv->driver.owner);
+
 	free_otherend_details(dev);
 
 	xenbus_switch_state(dev, XenbusStateClosed);