On Fri, Nov 20, 2020 at 03:48:48PM +0800, Qinglang Miao wrote:
> When put_device(&bridge->dev) being called, kfree(bridge) is inside
> of release function, so the following device_del would cause a
> use-after-free bug.
>
> Fixes: 37d6a0a6f470 ("PCI: Add pci_register_host_bridge() interface")
That commit did have some problems, but this patch doesn't apply to that
commit. See commits 1b54ae8327a4 and 9885440b16b8.
> Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
> Signed-off-by: Qinglang Miao <miaoqinglang@xxxxxxxxxx>
> ---
> drivers/pci/probe.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 4289030b0..82292e87e 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -991,8 +991,8 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
> return 0;
>
> unregister:
> - put_device(&bridge->dev);
> device_del(&bridge->dev);
> + put_device(&bridge->dev);
I don't think this is right.
Let's look at pci_register_host_bridge() with only the relevant
sections:
static int pci_register_host_bridge(struct pci_host_bridge *bridge)
{
...
err = device_add(&bridge->dev);
if (err) {
put_device(&bridge->dev);
goto free;
}
bus->bridge = get_device(&bridge->dev);
...
if (err)
goto unregister;
...
return 0;
unregister:
put_device(&bridge->dev);
device_del(&bridge->dev);
free:
kfree(bus);
return err;
}
The documentation for device_add says this:
* Rule of thumb is: if device_add() succeeds, you should call
* device_del() when you want to get rid of it. If device_add() has
* *not* succeeded, use *only* put_device() to drop the reference
* count.
The put_device at the end is to balance the get_device after device_add.
It will *only* decrement the use count. Then we call device_del as the
documentation says.
Rob
