[Linux-kernel-mentees] [PATCH v4] media/v4l2-core: Fix kernel-infoleak in video_put_user()

[Peilin Ye]

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 `ev32` and `vb32` using memset().

Cc: stable at vger.kernel.org
Fixes: 1a6c0b36dd19 ("media: v4l2-core: fix VIDIOC_DQEVENT for time64 ABI")
Fixes: 577c89b0ce72 ("media: v4l2-core: fix v4l2_buffer handling for time64 ABI")
Reported-and-tested-by: syzbot+79d751604cb6f29fbf59 at syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=79d751604cb6f29fbf59
Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Reviewed-by: Arnd Bergmann <arnd at arndb.de>
Signed-off-by: Peilin Ye <yepeilin.cs at gmail.com>
---
Change in v4:
    - Add `Cc:` and `Fixes:` tags. (Suggested by Arnd Bergmann <arnd at arndb.de>)

Change in v3:
    - Improve the commit description. (Suggested by Laurent Pinchart
      <laurent.pinchart at ideasonboard.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;
-- 
2.25.1