Re: [Linux-kernel-mentees] [PATCH v2] media/v4l2-core: Fix kernel-infoleak in video_put_user()

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Peilin,

Thank you for the patch.

On Sun, Jul 26, 2020 at 06:05:57PM -0400, Peilin Ye wrote:
> video_put_user() is copying uninitialized stack memory to userspace. Fix
> it by initializing `ev32` and `vb32` using memset().

How about mentioning that this is caused by the compiler not
initializing the holes ? Maybe something along the lines of

video_put_user() is copying uninitialized stack memory to userspace due
to the compiler not initializing holes in the structures declared on the
stack. Fix it by initializing the structures using memset().

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> Reported-and-tested-by: syzbot+79d751604cb6f29fbf59@syzkaller.appspotmail.com
> Link: https://syzkaller.appspot.com/bug?extid=79d751604cb6f29fbf59
> Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
> ---
> Change in v2:
>     - Do the same thing for `case VIDIOC_DQEVENT_TIME32`.
> 
>  drivers/media/v4l2-core/v4l2-ioctl.c | 50 +++++++++++++++-------------
>  1 file changed, 27 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index a556880f225a..e3a25ea913ac 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -3189,14 +3189,16 @@ static int video_put_user(void __user *arg, void *parg, unsigned int cmd)
>  #ifdef CONFIG_COMPAT_32BIT_TIME
>  	case VIDIOC_DQEVENT_TIME32: {
>  		struct v4l2_event *ev = parg;
> -		struct v4l2_event_time32 ev32 = {
> -			.type		= ev->type,
> -			.pending	= ev->pending,
> -			.sequence	= ev->sequence,
> -			.timestamp.tv_sec  = ev->timestamp.tv_sec,
> -			.timestamp.tv_nsec = ev->timestamp.tv_nsec,
> -			.id		= ev->id,
> -		};
> +		struct v4l2_event_time32 ev32;
> +
> +		memset(&ev32, 0, sizeof(ev32));
> +
> +		ev32.type	= ev->type;
> +		ev32.pending	= ev->pending;
> +		ev32.sequence	= ev->sequence;
> +		ev32.timestamp.tv_sec	= ev->timestamp.tv_sec;
> +		ev32.timestamp.tv_nsec	= ev->timestamp.tv_nsec;
> +		ev32.id		= ev->id;
>  
>  		memcpy(&ev32.u, &ev->u, sizeof(ev->u));
>  		memcpy(&ev32.reserved, &ev->reserved, sizeof(ev->reserved));
> @@ -3210,21 +3212,23 @@ static int video_put_user(void __user *arg, void *parg, unsigned int cmd)
>  	case VIDIOC_DQBUF_TIME32:
>  	case VIDIOC_PREPARE_BUF_TIME32: {
>  		struct v4l2_buffer *vb = parg;
> -		struct v4l2_buffer_time32 vb32 = {
> -			.index		= vb->index,
> -			.type		= vb->type,
> -			.bytesused	= vb->bytesused,
> -			.flags		= vb->flags,
> -			.field		= vb->field,
> -			.timestamp.tv_sec	= vb->timestamp.tv_sec,
> -			.timestamp.tv_usec	= vb->timestamp.tv_usec,
> -			.timecode	= vb->timecode,
> -			.sequence	= vb->sequence,
> -			.memory		= vb->memory,
> -			.m.userptr	= vb->m.userptr,
> -			.length		= vb->length,
> -			.request_fd	= vb->request_fd,
> -		};
> +		struct v4l2_buffer_time32 vb32;
> +
> +		memset(&vb32, 0, sizeof(vb32));
> +
> +		vb32.index	= vb->index;
> +		vb32.type	= vb->type;
> +		vb32.bytesused	= vb->bytesused;
> +		vb32.flags	= vb->flags;
> +		vb32.field	= vb->field;
> +		vb32.timestamp.tv_sec	= vb->timestamp.tv_sec;
> +		vb32.timestamp.tv_usec	= vb->timestamp.tv_usec;
> +		vb32.timecode	= vb->timecode;
> +		vb32.sequence	= vb->sequence;
> +		vb32.memory	= vb->memory;
> +		vb32.m.userptr	= vb->m.userptr;
> +		vb32.length	= vb->length;
> +		vb32.request_fd	= vb->request_fd;
>  
>  		if (copy_to_user(arg, &vb32, sizeof(vb32)))
>  			return -EFAULT;

-- 
Regards,

Laurent Pinchart