Re: [PATCH] tpm: tpm_nsc: Fix a double free of pdev in cleanup_nsc

Stefan Berger
2011-08-05T14:20:59Z

On 08/03/2011 07:58 PM, Axel Lin wrote:
> platform_device_unregister() will release all resources
> and remove it from the subsystem, then drop reference count by
> calling platform_device_put().
I also changed code into that direction in the recent patch to the
tpm_nsc driver. I didn't know whether that memory had to be freed or
not. Looking at several other drivers I found that none was freeing it
but calling platform_device_put() (which is also called by
platform_device_unregiser()) with the memory previously allocated via
platform_device_alloc(). Though platform_device_put() calls put_device()

http://lxr.linux.no/#linux+v3.0/drivers/base/platform.c#L138

which in turn calls kobject_put().

http://lxr.linux.no/#linux+v3.0/drivers/base/core.c#L1066

It was not clear to me whether the pdev memory would actually get freed
by kobject_put() -- but since other drivers were not freeing it
explicitly I wasn't sure. So either many drivers have a memory leak or
tpm_nsc was previously right about freeing it...

Stefan

> We should not call kfree(pdev) after platform_device_unregister(pdev).
>
> Signed-off-by: Axel Lin<axel.lin@gmail.com>
> ---
> drivers/char/tpm/tpm_nsc.c | 2 --
> 1 files changed, 0 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm_nsc.c b/drivers/char/tpm/tpm_nsc.c
> index 82facc9..4d24648 100644
> --- a/drivers/char/tpm/tpm_nsc.c
> +++ b/drivers/char/tpm/tpm_nsc.c
> @@ -396,8 +396,6 @@ static void __exit cleanup_nsc(void)
> if (pdev) {
> tpm_nsc_remove(&pdev->dev);
> platform_device_unregister(pdev);
> - kfree(pdev);
> - pdev = NULL;
> }
>
> platform_driver_unregister(&nsc_drv);