[PATCH 3/3] drm/msm/dsi: fix signedness bug in msm_dsi_host_cmd_rx()

[Dan Carpenter]

On Sat, Oct 02, 2021 at 01:59:56AM +0300, Dmitry Baryshkov wrote:
> On 01/10/2021 15:36, Dan Carpenter wrote:
> > The "msg->tx_len" variable is type size_t so if dsi_cmds2buf_tx()
> > returns a negative error code that it type promoted to a high positive
> > value and treat as a success.  The second problem with this code is
> > that it can return meaningless positive values on error.
> 
> It looks to me that this piece of code is not fully correct at all.
> dsi_cmds2bus_tx would return the size of DSI packet, not the size of the DSI
> buffer.

Ugh...  I misread what you were saying.  I was thinking I could just
check for negatives.  This sounds like struct_size() thing?

> 
> Could you please be more specific, which 'meaningless positive values' were
> you receiving?
> 

Returning any positive values at this point is a bug.  It's supposed to
return the number of bytes that were recieved.

And there is another bug as well:

drivers/gpu/drm/msm/dsi/dsi_host.c
  1370  static int dsi_cmds2buf_tx(struct msm_dsi_host *msm_host,
  1371                                  const struct mipi_dsi_msg *msg)
  1372  {
  1373          int len, ret;
  1374          int bllp_len = msm_host->mode->hdisplay *
  1375                          dsi_get_bpp(msm_host->format) / 8;
  1376  
  1377          len = dsi_cmd_dma_add(msm_host, msg);
  1378          if (!len) {

The dsi_cmd_dma_add() returns negative error codes so this check should
be "if (len <= 0) {".

  1379                  pr_err("%s: failed to add cmd type = 0x%x\n",
  1380                          __func__,  msg->type);
  1381                  return -EINVAL;
  1382          }
  1383  

I'm not sure about the size of "the DSI packet"  Could you handle this
one and give me a Reported-by tag?  That's probably simpler than another
back and forth on email.

regards,
dan carpenter