[Xen-devel] [PATCH v3 1/2] xen/xenbus: reference count registered modules

[Paul Durrant <pdurrant@xxxxxxxxxx>]

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>
---
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>

v2:
 - New in v2

v3:
 - Use try_module_get() rather than __module)get() and handle failure
 - Not added Juergen's R-b because of the change
---
 drivers/xen/xenbus/xenbus_probe.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/xenbus/xenbus_probe.c 
b/drivers/xen/xenbus/xenbus_probe.c
index 5b471889d723..4461f4583476 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -232,9 +232,16 @@ 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) {
@@ -244,6 +251,8 @@ 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);
@@ -263,6 +272,8 @@ 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);
-- 
2.20.1


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