On 23.01.2018 09:32, Dan Carpenter wrote:
> 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:658 vidioc_dqbuf()
> error: buffer overflow 'ctx->dst_bufs' 32 user_rl = '0-u32max'
>
> drivers/media/platform/s5p-mfc/s5p_mfc_dec.c
> 635 /* Dequeue a buffer */
> 636 static int vidioc_dqbuf(struct file *file, void *priv, struct v4l2_buffer *buf)
> 637 {
> 638 const struct v4l2_event ev = {
> 639 .type = V4L2_EVENT_EOS
> 640 };
> 641 struct s5p_mfc_ctx *ctx = fh_to_ctx(priv);
> 642 int ret;
> 643
> 644 if (ctx->state == MFCINST_ERROR) {
> 645 mfc_err_limited("Call on DQBUF after unrecoverable error\n");
> 646 return -EIO;
> 647 }
> 648
> 649 switch (buf->type) {
> 650 case V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE:
> 651 return vb2_dqbuf(&ctx->vq_src, buf, file->f_flags & O_NONBLOCK);
> 652 case V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE:
> 653 ret = vb2_dqbuf(&ctx->vq_dst, buf, file->f_flags & O_NONBLOCK);
> 654 if (ret)
> 655 return ret;
> 656
> 657 if (ctx->state == MFCINST_FINISHED &&
> 658 (ctx->dst_bufs[buf->index].flags & MFC_BUF_FLAG_EOS))
> ^^^^^^^^^^
> Smatch is complaining that "buf->index" is not capped. So far as I can
> see this is true. I would have expected it to be checked in
> check_array_args() or video_usercopy() but I couldn't find the check.
I did not work in V4L2 area for long time, so I could be wrong, but I
hope the code is correct, below my explanation.
User provides only type, memory and reserved fields in buf, other fields
are filled by vb2_dqbuf (line 653) core function, ie index field is
copied from buffer which was queued by qbuf.
And vidioc_qbuf calls vb2_qbuf, which calls vb2_queue_or_prepare_buf,
which checks index bounds [1].
So I suppose this code is correct.
Btw, I have also looked at other drivers and it looks omap driver
handles it incorrectly, ie it uses index field provided by user -
possible memory leak. CC Hans and Mauro, since there is no driver
maintainer of OMAP.
Btw2, is it possible to check in smatch which fields of passed struct
given callback can read or fill ? For example here API restrict dqbuf
callback to read only three fields of buf, and fill the others.
[1]:
http://elixir.free-electrons.com/linux/latest/source/drivers/media/v4l2-core/videobuf2-v4l2.c#L165
[2]:
http://elixir.free-electrons.com/linux/latest/source/drivers/media/platform/omap/omap_vout.c#L1520
Regards
Andrzej
>
> 659 v4l2_event_queue_fh(&ctx->fh, &ev);
> 660 return 0;
> 661 default:
> 662 return -EINVAL;
> 663 }
> 664 }
>
>
> regards,
> dan carpenter
>
>
>
