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")
Reported-by: Hulk Robot <[email protected]>
Signed-off-by: Qinglang Miao <[email protected]>
---
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);
free:
kfree(bus);
--
2.23.0
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 <[email protected]>
> Signed-off-by: Qinglang Miao <[email protected]>
> ---
> 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
?? 2020/12/11 23:46, Rob Herring ะด??:
> 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 <[email protected]>
>> Signed-off-by: Qinglang Miao <[email protected]>
>> ---
>> 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
> .
Hi, Rob
Your words make sence to me: the code is *logicly* correct here and
won't raise a use-after-free bug. I do hold a misunderstanding of this
one, sorry for that ~
But I still think this patch should be reconsidered:
The kdoc of device_unregister explicitly mentions the possibility that
other refs might continue to exist after device_unregister was called,
and *del_device* is first part of it.
By the way, 'del_device() called before put_device()' is everywhere in
kernel code, like device_unregister(), pci_destroy_dev() or
switchtec_pci_remove()
In fact, I can't find another place in kernel code looks like:
put_device(x);
device_del(x);
So I guess put_device() ought to be the last time we touch the object
(I don't find evidence strong enough in kdoc to prove this) and putting
put_device after device_del is a more natural logic.
Qinglang
.
>