spi: Fix potential NULL pointer dereference in spi_shutdown()

Shutdown bus function might be called on the unbound device, so add a
check if there is a driver before calling its shutdown function.

This fixes following kernel panic obserbed during system reboot:
Unable to handle kernel NULL pointer dereference at virtual address 0000000000000018
...
Call trace:
 spi_shutdown+0x10/0x38
 kernel_restart_prepare+0x34/0x40
 kernel_restart+0x14/0x88
 __do_sys_reboot+0x148/0x248
 __arm64_sys_reboot+0x1c/0x28
 el0_svc_common.constprop.3+0x74/0x198
 do_el0_svc+0x20/0x98
 el0_sync_handler+0x140/0x1a8
 el0_sync+0x140/0x180
Code: f9403402 d1008041 f100005f 9a9f1021 (f9400c21)
---[ end trace 266c07205a2d632e ]---

Fixes: 9db34ee64ce4 (spi: Use bus_type functions for probe, remove and shutdown)
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20201124131523.32287-1-m.szyprowski@samsung.com
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 6ee0f66..1564914 100644 (file)
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -426,10 +426,12 @@ static int spi_remove(struct device *dev)
 
 static void spi_shutdown(struct device *dev)
 {
-       const struct spi_driver         *sdrv = to_spi_driver(dev->driver);
+       if (dev->driver) {
+               const struct spi_driver *sdrv = to_spi_driver(dev->driver);
 
-       if (sdrv->shutdown)
-               sdrv->shutdown(to_spi_device(dev));
+               if (sdrv->shutdown)
+                       sdrv->shutdown(to_spi_device(dev));
+       }
 }
 
 struct bus_type spi_bus_type = {