[PATCH 1/3] spi: fix use-after-free at controller deregistration

[Johan Hovold]

The controller is typically freed as part of device_unregister() so
store the bus id before deregistration to avoid use-after-free when the
id is later released.

Fixes: 9b61e302210e ("spi: Pick spi bus number from Linux idr or spi alias")
Cc: stable <sta...@vger.kernel.org>     # 4.13
Cc: Suniel Mahesh <suni...@techveda.org>
Cc: Karthik Tummala <kart...@techveda.org>
Signed-off-by: Johan Hovold <jo...@kernel.org>
---
 drivers/spi/spi.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index e8b5a5e21b2e..3ff0ee88c467 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -2245,11 +2245,12 @@ static int __unregister(struct device *dev, void *null)
 void spi_unregister_controller(struct spi_controller *ctlr)
 {
        struct spi_controller *found;
+       int id = ctlr->bus_num;
        int dummy;
 
        /* First make sure that this controller was ever added */
        mutex_lock(&board_lock);
-       found = idr_find(&spi_master_idr, ctlr->bus_num);
+       found = idr_find(&spi_master_idr, id);
        mutex_unlock(&board_lock);
        if (found != ctlr) {
                dev_dbg(&ctlr->dev,
@@ -2269,7 +2270,7 @@ void spi_unregister_controller(struct spi_controller 
*ctlr)
        device_unregister(&ctlr->dev);
        /* free bus id */
        mutex_lock(&board_lock);
-       idr_remove(&spi_master_idr, ctlr->bus_num);
+       idr_remove(&spi_master_idr, id);
        mutex_unlock(&board_lock);
 }
 EXPORT_SYMBOL_GPL(spi_unregister_controller);
-- 
2.14.3