block: ioctl: fix information leak to userland

Structure hd_geometry is copied to userland with 4 padding bytes
between cylinders and start fields uninitialized on 64-bit platforms.
It leads to leaking of contents of kernel stack memory.

Currently there is no memset() in real implementations of getgeo()
in drivers/block/, so it makes sense to have memset() in blkdev_ioctl().

Signed-off-by: Vasiliy Kulikov <segooon@gmail.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/block/ioctl.c b/block/ioctl.c
index 38aa194f63ec..3d866d0037f2 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -242,6 +242,7 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
                  * We need to set the startsect first, the driver may
                  * want to override it.
                  */
+                memset(&geo, 0, sizeof(geo));
                 geo.start = get_start_sect(bdev);
                 ret = disk->fops->getgeo(bdev, &geo);
                 if (ret)