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

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Message-ID: <20171029124328.GE4240@vireshk-i7>
Date:   Sun, 29 Oct 2017 18:13:28 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Rui Miguel Silva <rmfrfs@...il.com>,
        Viresh Kumar <vireshk@...nel.org>,
        Alex Elder <elder@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        greybus-dev@...ts.linaro.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, stable <stable@...r.kernel.org>
Subject: Re: [PATCH] staging: greybus: spilib: fix use-after-free after
 deregistration

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@...r.kernel.org>     # 4.9
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Signed-off-by: Johan Hovold <johan@...nel.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@...aro.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