Re: [PATCH] ALSA: fix kernel panic in initialization of mpu401 driver

[Alan Stern]

On Thu, 5 Oct 2006, Jaroslav Kysela wrote:

> On Wed, 4 Oct 2006, Jiri Kosina wrote:
> 
> > I am getting kernel panic (NULL pointer dereference) on boot, with kernel 
> > compiled with CONFIG_SND_MPU401_UART=y, on machine which does not have 
> > this piece of hardware.
> > 
> > I have traced the problem down to 
> > sound/drivers/mpu401/mpu401.c:snd_mpu401_probe() returning EINVAL, when 
> > either port or IRQ parameters are not specified.
> > 
> > In such case, the drivers/base/bus.c:bus_attach_device() does not perform 
> > klist_add_tail() call, but rather sets dev->is_registered to 0. This flag 
> > is however not checked by the driver, so later on, when 
> > alsa_card_mpu401_init() is called and platform_device_register_simple() 
> > fails, the following callchain happens, causing NULL pointer dereference: 
> > alsa_card_mpu401_init() -> platform_device_unregister() -> 
> > platform_device_del() -> device_del() -> bus_remove_device() -> 
> > klist_del() -> BOOM (the entry was not added to klist in 
> > bus_attach_device()).
> > 
> > Proper solution is returning ENODEV from the ->probe() routine, which will 
> > be correctly handled then by the rest of the device-driver attaching 
> > subsystem (namely the retval check in bus_attach_device()). The following 
> > patch fixes the problem, please apply.
> 
> Unfortunately, I do not think that it's a proper solution. I think that
> platform device layer should play more nicely and if probe() fails for 
> a reason and if platform_device_register_simple() does not set 
> IS_ERR(), then platform_device_unregister() must be callable to free
> all resources.
> 
> Also, you've proposed to not fix all returns in snd_mpu401_probe() only 
> first two.
> 
> I would reject this patch and fix drivers/base/bus.c. The problematic 
> change is in commit f2eaae197f4590c4d96f31b09b0ee9067421a95c and this 
> patch will probably fix it:

Your patch is right as far as it goes, but it misses part of the problem.  
device_add() shouldn't ignore the return value from bus_attach_device().  
That's why we ended up trying to unregister a device which never was 
properly registered in the first place.

What do you think of this addition to your patch (untested)?

Alan Stern


Index: 18g20/drivers/base/bus.c
===================================================================
--- 18g20.orig/drivers/base/bus.c
+++ 18g20/drivers/base/bus.c
@@ -453,8 +453,10 @@ void bus_remove_device(struct device * d
 		remove_deprecated_bus_links(dev);
 		sysfs_remove_link(&dev->bus->devices.kobj, dev->bus_id);
 		device_remove_attrs(dev->bus, dev);
-		dev->is_registered = 0;
-		klist_del(&dev->knode_bus);
+		if (dev->is_registered) {
+			dev->is_registered = 0;
+			klist_del(&dev->knode_bus);
+		}
 		pr_debug("bus %s: remove device %s\n", dev->bus->name, dev->bus_id);
 		device_release_driver(dev);
 		put_bus(dev->bus);
Index: 18g20/drivers/base/core.c
===================================================================
--- 18g20.orig/drivers/base/core.c
+++ 18g20/drivers/base/core.c
@@ -485,7 +485,8 @@ int device_add(struct device *dev)
 	if ((error = bus_add_device(dev)))
 		goto BusError;
 	kobject_uevent(&dev->kobj, KOBJ_ADD);
-	bus_attach_device(dev);
+	if ((error = bus_attach_device(dev)))
+		goto AttachError;
 	if (parent)
 		klist_add_tail(&dev->knode_parent, &parent->klist_children);
 
@@ -504,6 +505,8 @@ int device_add(struct device *dev)
  	kfree(class_name);
 	put_device(dev);
 	return error;
+ AttachError:
+	bus_remove_device(dev);
  BusError:
 	device_pm_remove(dev);
  PMError:

-
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