Calling freeze_bdev() twice on the same block device without mounted filesystem get_super() will return NULL, which will lead to NULL-ptr dereference later in drop_super().
Check get_super() result to fix that. Note, that this is a purely theoretical issue. We have only 3 freeze_bdev() callers. 2 of them are in filesystem code and used on a device with mounted fs. The third one in lock_fs() has protection in upper-layer code against freezing block device the second time without thawing it first. Signed-off-by: Andrey Ryabinin <[email protected]> --- fs/block_dev.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/block_dev.c b/fs/block_dev.c index c3cdde8..c18b083 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -249,7 +249,8 @@ struct super_block *freeze_bdev(struct block_device *bdev) * thaw_bdev drops it. */ sb = get_super(bdev); - drop_super(sb); + if (sb) + drop_super(sb); mutex_unlock(&bdev->bd_fsfreeze_mutex); return sb; } -- 2.7.3
