media: v4l2-core: explicitly clear ioctl input data

commit 7b53cca764f9b291b7907fcd39d9e66ad728ee0b upstream.

As seen from a recent syzbot bug report, mistakes in the compat ioctl
implementation can lead to uninitialized kernel stack data getting used
as input for driver ioctl handlers.

The reported bug is now fixed, but it's possible that other related
bugs are still present or get added in the future. As the drivers need
to check user input already, the possible impact is fairly low, but it
might still cause an information leak.

To be on the safe side, always clear the entire ioctl buffer before
calling the conversion handler functions that are meant to initialize
them.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
index 7e8bf4b1ab2e5f16c2d102985ad79400627b7d43..efdf6a5475cb390f68e90d7a14311e8024b0527f 100644 (file)
--- a/drivers/media/v4l2-core/v4l2-ioctl.c
+++ b/drivers/media/v4l2-core/v4l2-ioctl.c
@@ -3166,8 +3166,10 @@ static int video_get_user(void __user *arg, void *parg,
                if (copy_from_user(parg, (void __user *)arg, n))
                        err = -EFAULT;
        } else if (in_compat_syscall()) {
+               memset(parg, 0, n);
                err = v4l2_compat_get_user(arg, parg, cmd);
        } else {
+               memset(parg, 0, n);
 #if !defined(CONFIG_64BIT) && defined(CONFIG_COMPAT_32BIT_TIME)
                switch (cmd) {
                case VIDIOC_QUERYBUF_TIME32: