media: dvb_vb2: fix possible out of bound access

vb2_core_qbuf and vb2_core_querybuf don't check the range of b->index
controlled by the user.

Fix this by adding range checking code before using them.

Fixes: 57868acc369a ("media: videobuf2: Add new uAPI for DVB streaming I/O")
Signed-off-by: Hangyu Hua <[e-mail]>
Reviewed-by: Sergey Senozhatsky <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/dvb-core/dvb_vb2.c

···
 
 int dvb_vb2_querybuf(struct dvb_vb2_ctx *ctx, struct dmx_buffer *b)
 {
+	struct vb2_queue *q = &ctx->vb_q;
+
+	if (b->index >= q->num_buffers) {
+		dprintk(1, "[%s] buffer index out of range\n", ctx->name);
+		return -EINVAL;
+	}
 	vb2_core_querybuf(&ctx->vb_q, b->index, b);
 	dprintk(3, "[%s] index=%d\n", ctx->name, b->index);
 	return 0;
···
 
 int dvb_vb2_qbuf(struct dvb_vb2_ctx *ctx, struct dmx_buffer *b)
 {
+	struct vb2_queue *q = &ctx->vb_q;
 	int ret;
 
+	if (b->index >= q->num_buffers) {
+		dprintk(1, "[%s] buffer index out of range\n", ctx->name);
+		return -EINVAL;
+	}
 	ret = vb2_core_qbuf(&ctx->vb_q, b->index, b, NULL);
 	if (ret) {
 		dprintk(1, "[%s] index=%d errno=%d\n", ctx->name,