[PATCH] mtd: physmap_of: fix potential NULL dereference

[Ard Biesheuvel]

On device remove, when testing the cmtd field of an of_flash
struct to decide whether it is a concatenated device or not,
we get a false positive on cmtd == NULL, and dereference it
subsequently. This may occur if of_flash_remove() is called
from the cleanup path of of_flash_probe().

Instead, test for NULL first, and only then perform the test
for a concatenated device.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
 drivers/mtd/maps/physmap_of.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/mtd/maps/physmap_of.c b/drivers/mtd/maps/physmap_of.c
index c1d21cb501ca..e48930424091 100644
--- a/drivers/mtd/maps/physmap_of.c
+++ b/drivers/mtd/maps/physmap_of.c
@@ -47,14 +47,12 @@ static int of_flash_remove(struct platform_device *dev)
 		return 0;
 	dev_set_drvdata(&dev->dev, NULL);
 
-	if (info->cmtd != info->list[0].mtd) {
+	if (info->cmtd) {
 		mtd_device_unregister(info->cmtd);
-		mtd_concat_destroy(info->cmtd);
+		if (info->cmtd != info->list[0].mtd)
+			mtd_concat_destroy(info->cmtd);
 	}
 
-	if (info->cmtd)
-		mtd_device_unregister(info->cmtd);
-
 	for (i = 0; i < info->list_size; i++) {
 		if (info->list[i].mtd)
 			map_destroy(info->list[i].mtd);
-- 
1.8.3.2