re: drm/bridge: it6505: fix HDCP CTS compare V matching

re: drm/bridge: it6505: fix HDCP CTS compare V matching

[Colin King (gmail)]

Hi,

static analysis on Linux-next has found a potential issue with the 
following commit:

commit 0989c02c7a5c887c70deafen80c64d0291624e1a7
Author: Hermes Wu <hermes.wu@ite.com.tw>
Date:   Mon Dec 30 18:51:26 2024 +0800

     drm/bridge: it6505: fix HDCP CTS compare V matching


The issue is as follows:

Source: drivers/gpu/drm/bridge/ite-it6505.c, function: 
it6505_hdcp_part2_ksvlist_check:

             for (i = 0; i < 5; i++) {
                    if (bv[i][3] != av[i][0] || bv[i][2] != av[i][1] ||
                        av[i][1] != av[i][2] || bv[i][0] != av[i][3])
                             break;

                     DRM_DEV_DEBUG_DRIVER(dev, "V' all match!! %d, %d", 
retry, i);
                     return true;
             }


in the above for-loop, only iteration with i = 0 is performed, either 
the if statement breaks out of the loop if the condition is true or
we reach the return true statement. Both conditions means the loop is 
never iterated, yet the loop is expected to iterate for 5 times. This 
looks incorrect.

Colin

RE: drm/bridge: it6505: fix HDCP CTS compare V matching

[Hermes.Wu]

Hi

>-----Original Message-----
>From: Colin King (gmail) <colin.i.king@gmail.com> 
>Sent: Tuesday, January 7, 2025 5:31 PM
>To: Hermes Wu (吳佳宏) <Hermes.Wu@ite.com.tw>
>Cc: Andrzej Hajda <andrzej.hajda@intel.com>; Neil Armstrong <neil.armstrong@linaro.org>; Robert Foss <rfoss@kernel.org>; Laurent Pinchart <Laurent.pinchart@ideasonboard.com>; Jonas Karlman <jonas@kwiboo.se>; Jernej Skrabec <jernej.skrabec@gmail.com>; dri-devel@lists.freedesktop.org; linux-kernel@vger.kernel.org
>Subject: re: drm/bridge: it6505: fix HDCP CTS compare V matching
>
>Hi,
>
>static analysis on Linux-next has found a potential issue with the following commit:
>
>commit 0989c02c7a5c887c70deafen80c64d0291624e1a7
>Author: Hermes Wu <hermes.wu@ite.com.tw>
>Date:   Mon Dec 30 18:51:26 2024 +0800
>
>     drm/bridge: it6505: fix HDCP CTS compare V matching
>
>
>The issue is as follows:
>
>Source: drivers/gpu/drm/bridge/ite-it6505.c, function: 
>it6505_hdcp_part2_ksvlist_check:
>
>             for (i = 0; i < 5; i++) {
>                    if (bv[i][3] != av[i][0] || bv[i][2] != av[i][1] ||
>                        av[i][1] != av[i][2] || bv[i][0] != av[i][3])
>                             break;
>
>                     DRM_DEV_DEBUG_DRIVER(dev, "V' all match!! %d, %d", retry, i);
>                     return true;
>             }

It should check if the for loop reach i == 4 before return true.

I will fix it,

thanks

>
>in the above for-loop, only iteration with i = 0 is performed, either 
>the if statement breaks out of the loop if the condition is true or
>we reach the return true statement. Both conditions means the loop is 
>never iterated, yet the loop is expected to iterate for 5 times. This 
>looks incorrect.
>
>Colin
>

>
>