[PATCH] block: ioctl: fix information leak to userland

[Vasiliy Kulikov <segooon@gmail.com>]

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>
---
 block/ioctl.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/block/ioctl.c b/block/ioctl.c
index d724ceb..60bae81 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)
-- 
1.7.0.4