mtd: physmap_of: fix potential NULL dereference

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Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=92b633a8a482c4bc1ff3b7cffdcace7836861554
Commit:     92b633a8a482c4bc1ff3b7cffdcace7836861554
Parent:     58c81957b7d284c57a9fc1b815c77155ef744ea5
Author:     Ard Biesheuvel <ard.biesheuvel at linaro.org>
AuthorDate: Sun Nov 30 13:51:03 2014 +0100
Committer:  Brian Norris <computersforpeace at gmail.com>
CommitDate: Fri Dec 12 19:12:16 2014 -0800

    mtd: physmap_of: fix potential NULL dereference
    
    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>
    Signed-off-by: Brian Norris <computersforpeace at gmail.com>
---
 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 c1d21cb..e489304 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);