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

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

[Johan Hovold]

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@vger.kernel.org>     # 4.9
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 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);
 
-- 
2.14.3

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

[Viresh Kumar]

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@vger.kernel.org>     # 4.9
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Johan Hovold <johan@kernel.org>
> ---
>  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@linaro.org>

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

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

[Johan Hovold]

On Sun, Oct 29, 2017 at 06:13:28PM +0530, Viresh Kumar wrote:
> 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@vger.kernel.org>     # 4.9
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Signed-off-by: Johan Hovold <johan@kernel.org>

> Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
> 
> While looking at this I think I found another problem (I will send it as a
> separate patch later on) and this fixes it:

That's right, and I already posted a fix for that use-after-free:

	https://lkml.kernel.org/r/20171029115625.32385-1-johan@kernel.org

Thanks,
Johan

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

[Viresh Kumar]

On 29-10-17, 13:51, Johan Hovold wrote:
> That's right, and I already posted a fix for that use-after-free:
> 
> 	https://lkml.kernel.org/r/20171029115625.32385-1-johan@kernel.org

Great :)

-- 
viresh

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

[Rui Miguel Silva]

Hi Johan,
Thanks for the patch.

On Sun 29 Oct 2017 at 12:01, Johan Hovold <johan@kernel.org> 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@vger.kernel.org>     # 4.9
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Johan Hovold <johan@kernel.org>

Reviewed-by: Rui Miguel Silva <rmfrfs@gmail.com>

---
Cheers,
	Rui

> ---
>  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);