Messages in this thread |  | | From | "Adam J. Richter" <> | Date | Sun, 23 Sep 2001 14:21:59 -0700 | Subject | Re: PATCH: linux-2.4.10-pre14/drivers/sound/maestro.c ignored pci_module_init results |
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>> = Adam Richter > = Marcus Meissner
>> The initialization routine in >> linux-2.4.10-pre14/drivers/sound/maestro.c ignores the return value >> from pci_module_init, and allows module initialization to succeed >> even if pci_module_init failed. pci_module_init fails and unloads >> the driver if the caller is a module and there is no matching hardware. >> Because maestro.c ignored this failure, loading maestro.o on a system >> where the corresponding alsa driver was already loaded or on a system >> without matchin hardware would result in a kernel null pointer dereference >> in pci_unregister_driver when the module is unloaded or when one >> attempts to reboot the system (i.e., when the module attempt to >> unregister a PCI driver that is not registered).
>Why and where does it Oops?
On a machine that has no maestro hardware or that already has the alsa drivers bound to the maestro PCI hardware, either of the following will cause a null pointer dereference when pci_unregister_driver tries to unregister a driver that is not registered:
modprobe maestro rmmod maestro
(as cleanup_maestro incorrectly calls pci_unregister_driver on a PCI driver that is not loaded.)
...or...
modprobe meastro reboot
(as maestro_notifier incorrectly calls pci_unregister_driver on a PCI driver that is not loaded.)
I experimentally verified both of these on a machine that already had the maestro ALSA drivers loaded. I assume the null pointer dereference would be from the list_del(&drv->node) in pci_unregister_driver, since list_del calls __list_del, which assumes that drv->node->{prev,next} are not NULL, but they would have been set to NULL by the first pci_remove_module, which pci_module_init called when the driver failed to bind to anything, but which the maestro driver incorrectly ignored.
>The code for pci_unregister_driver in >drivers/pci/pci.c looks correct and should not Oops. > >The reboot notifier might be problematic, but I have not checked it.
There is nothing wrong with pci_unregister_driver. The bug is where init_maestro in maestro.c ignored the results of pci_module_init, which is what my patch fixes.
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