Re: [PATCH 0/8] counter: Remove struct counter_device::priv

On 12/21/21 12:35 PM, Uwe Kleine-König wrote:

Hello Lars,

On Tue, Dec 21, 2021 at 12:12:12PM +0100, Lars-Peter Clausen wrote:

quoted

On 12/21/21 11:45 AM, Uwe Kleine-König wrote:

quoted

similar to patch
https://lore.kernel.org/r/4bde7cbd9e43a5909208102094444219d3154466.1640072891.git.vilhelm.gray@gmail.com (local)
the usage of struct counter_device::priv can be replaced by
container_of which improves type safety and code size.

This series depends on above patch, converts the remaining drivers and
finally drops struct counter_device::priv.

Not sure if this is such a good idea. struct counter_device should not be
embedded in the drivers state struct in the first place.

Just to mention it: My patch series didn't change this, this was already
broken before.

I know, but this series has to be reverted when the framework is fixed.

quoted

struct counter_device contains a struct device, which is a reference counted
object. But by embedding it in the driver state struct the life time of both
the struct counter_device and and struct device are bound to the life time
of the driver state struct.

Which means the struct device memory can get freed before the last reference
is dropped, which leads to a use-after-free and undefined behavior.

Well, the driver struct is allocated using devm_kzalloc for all drivers.

devm_kzalloc() doesn't make a difference. The managed memory is freed 
when the parent device is unbound/removed. There may very well be 
reference to the counter_device at this point.

So I think it's not *very* urgent to fix. Still you're right, this
should be addressed.

Yes and no, this can trivially be used for privilege escalation, but 
then again on systems with a counter_device probably everything runs as 
root anyway.

quoted

The framework should be changed to rather then embedding the struct
counter_device in the state struct to just have a pointer to it. With the
struct counter_device having its own allocation that will be freed when the
last reference to the struct device is dropped.

My favourite would be to implement a counter_device_alloc /
counter_device_add approach, similar to what spi_alloc_controller and
alloc_etherdev do. The downside is that this isn't typesafe either :-\

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