[bug report] [media] s5p-mfc: use MFC_BUF_FLAG_EOS to identify last buffers in decoder capture queue

[Dan Carpenter <dan.carpenter@oracle.com>]

Hello Andrzej Hajda,

The patch 4d0b0ed63660: "[media] s5p-mfc: use MFC_BUF_FLAG_EOS to
identify last buffers in decoder capture queue" from Oct 7, 2015,
leads to the following static checker warning:

	drivers/media/platform/s5p-mfc/s5p_mfc_dec.c:664 vidioc_dqbuf()
	warn: uncapped user index 'ctx->dst_bufs[buf->index]'

drivers/media/platform/s5p-mfc/s5p_mfc_dec.c
    642 static int vidioc_dqbuf(struct file *file, void *priv, struct v4l2_buffer *buf)
    643 {
    644 	const struct v4l2_event ev = {
    645 		.type = V4L2_EVENT_EOS
    646 	};
    647 	struct s5p_mfc_ctx *ctx = fh_to_ctx(priv);
    648 	int ret;
    649 
    650 	if (ctx->state == MFCINST_ERROR) {
    651 		mfc_err_limited("Call on DQBUF after unrecoverable error\n");
    652 		return -EIO;
    653 	}
    654 
    655 	switch (buf->type) {
    656 	case V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE:
    657 		return vb2_dqbuf(&ctx->vq_src, buf, file->f_flags & O_NONBLOCK);
    658 	case V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE:
    659 		ret = vb2_dqbuf(&ctx->vq_dst, buf, file->f_flags & O_NONBLOCK);
    660 		if (ret)
    661 			return ret;
    662 
    663 		if (ctx->state == MFCINST_FINISHED &&
--> 664 		    (ctx->dst_bufs[buf->index].flags & MFC_BUF_FLAG_EOS))
                                           ^^^^^^^^^^
Smatch is saying that this isn't capped.  The truth is that v4l2 code is
a bit complicated for Smatch, but in this case I can't see where
"buf->index" does get capped.  I would have expected it to be capped in
check_array_args() where we check "buf->length" but it's not.

I've been going through these warnings really carefully in the past
couple weeks trying to fix false positives so let me know what I'm
missing and I will update the check.  Even if I have to manually muck
in the DB.

    665 			v4l2_event_queue_fh(&ctx->fh, &ev);
    666 		return 0;
    667 	default:
    668 		return -EINVAL;
    669 	}
    670 }

regards,
dan carpenter