Re: [PATCH] staging: greybus: spilib: fix use-after-free after deregistration

From: Viresh Kumar
Date: Sun Oct 29 2017 - 08:44:02 EST


On 29-10-17, 13:01, Johan Hovold wrote:
> Remove erroneous spi_master_put() after controller deregistration which
> would access the already freed spi controller.
>
> Note that spi_unregister_master() drops our only controller reference.
>
> Fixes: ba3e67001b42 ("greybus: SPI: convert to a gpbridge driver")
> Cc: stable <stable@xxxxxxxxxxxxxxx> # 4.9
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
> ---
> drivers/staging/greybus/spilib.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/staging/greybus/spilib.c b/drivers/staging/greybus/spilib.c
> index e97b19148497..1e7321a1404c 100644
> --- a/drivers/staging/greybus/spilib.c
> +++ b/drivers/staging/greybus/spilib.c
> @@ -544,11 +544,14 @@ int gb_spilib_master_init(struct gb_connection *connection, struct device *dev,
>
> return 0;
>
> -exit_spi_unregister:
> - spi_unregister_master(master);
> exit_spi_put:
> spi_master_put(master);
>
> + return ret;
> +
> +exit_spi_unregister:
> + spi_unregister_master(master);
> +
> return ret;
> }
> EXPORT_SYMBOL_GPL(gb_spilib_master_init);
> @@ -558,7 +561,6 @@ void gb_spilib_master_exit(struct gb_connection *connection)
> struct spi_master *master = gb_connection_get_data(connection);
>
> spi_unregister_master(master);
> - spi_master_put(master);
> }
> EXPORT_SYMBOL_GPL(gb_spilib_master_exit);

Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>

While looking at this I think I found another problem (I will send it as a
separate patch later on) and this fixes it:

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 6e65524cbfd9..af7ca751b4f7 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -2261,11 +2261,11 @@ void spi_unregister_controller(struct spi_controller *ctlr)
mutex_unlock(&board_lock);

dummy = device_for_each_child(&ctlr->dev, NULL, __unregister);
- device_unregister(&ctlr->dev);
/* free bus id */
mutex_lock(&board_lock);
idr_remove(&spi_master_idr, ctlr->bus_num);
mutex_unlock(&board_lock);
+ device_unregister(&ctlr->dev);
}
EXPORT_SYMBOL_GPL(spi_unregister_controller);

--
viresh