Re: [PATCH 1/2] devcoredump: Remove devcoredump device if failing device is gone

[Souza, Jose]

On Fri, 2024-01-26 at 10:11 -0500, Rodrigo Vivi wrote:
> Make dev_coredumpm a real device managed helper, that not only
> frees the device after a scheduled delay (DEVCD_TIMEOUT), but
> also when the failing/crashed device is gone.
> 
> The module remove for the drivers using devcoredump are currently
> broken if attempted between the crash and the DEVCD_TIMEOUT, since
> the symbolic sysfs link won't be deleted.
> 
> On top of that, for PCI devices, the unbind of the device will
> call the pci .remove void function, that cannot fail. At that
> time, our device is pretty much gone, but the read and free
> functions are alive trough the devcoredump device and they
> can get some NULL dereferences or use after free.
> 
> So, if the failing-device is gone let's also request for the
> devcoredump-device removal using the same mod_delayed_work
> as when writing anything through data. The flush cannot be
> used since it is synchronous and the devcd would be surely
> gone right before the mutex_unlock on the next line.
> 
> 
> 

Reviewed-by: José Roberto de Souza <jose.souza@xxxxxxxxx>

> Cc: Jose Souza <jose.souza@xxxxxxxxx>
> Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Cc: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Rafael J. Wysocki <rafael@xxxxxxxxxx>
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> ---
>  drivers/base/devcoredump.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/drivers/base/devcoredump.c b/drivers/base/devcoredump.c
> index 7e2d1f0d903a..678ecc2fa242 100644
> --- a/drivers/base/devcoredump.c
> +++ b/drivers/base/devcoredump.c
> @@ -304,6 +304,19 @@ static ssize_t devcd_read_from_sgtable(char *buffer, loff_t offset,
>  				  offset);
>  }
>  
> +static void devcd_remove(void *data)
> +{
> +	struct devcd_entry *devcd = data;
> +
> +	mutex_lock(&devcd->mutex);
> +	if (!devcd->delete_work) {
> +		devcd->delete_work = true;
> +		/* XXX: Cannot flush otherwise the mutex below will hit a UAF */
> +		mod_delayed_work(system_wq, &devcd->del_wk, 0);
> +	}
> +	mutex_unlock(&devcd->mutex);
> +}
> +
>  /**
>   * dev_coredumpm - create device coredump with read/free methods
>   * @dev: the struct device for the crashed device
> @@ -381,6 +394,8 @@ void dev_coredumpm(struct device *dev, struct module *owner,
>  	kobject_uevent(&devcd->devcd_dev.kobj, KOBJ_ADD);
>  	INIT_DELAYED_WORK(&devcd->del_wk, devcd_del);
>  	schedule_delayed_work(&devcd->del_wk, DEVCD_TIMEOUT);
> +	if (devm_add_action(dev, devcd_remove, devcd))
> +		dev_warn(dev, "devcoredump managed auto-removal registration failed\n");
>  	mutex_unlock(&devcd->mutex);
>  	return;
>   put_device: