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From:   Won Chung <wonchung@google.com>
Date:   Tue, 26 Apr 2022 01:56:55 +0900
Message-ID: <CAOvb9yjCnw=-5wO5_X6ond3GFdpRaNUPyyzojE49zTGfaWNNsg@mail.gmail.com>
Subject: Re: [PATCH 1/2] misc/mei: Add NULL check to component match callback functions
To:     Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        Alexander Usyskin <alexander.usyskin@intel.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Benson Leung <bleung@chromium.org>,
        Prashant Malani <pmalani@chromium.org>,
        Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>,
        linux-kernel@vger.kernel.org,
        "Winkler, Tomas" <tomas.winkler@intel.com>
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On Tue, Apr 19, 2022 at 2:59 AM Won Chung <wonchung@google.com> wrote:
>
> Currently, component_match callback functions used in mei refers to the
> driver name, assuming that the component device being matched has a
> driver bound. It can cause a NULL pointer dereference when a device
> without a driver bound registers a component. This is due to the nature
> of the component framework where all registered components are matched
> in any component_match callback functions. So even if a component is
> registered by a totally irrelevant device, that component is also
> shared to these callbacks for i915 driver.
>
> To prevent totally irrelevant device being matched for i915 and causing
> a NULL pointer dereference for checking driver name, add a NULL check on
> dev->driver to check if there is a driver bound before checking the
> driver name.
>
> In the future, the string compare on the driver name, "i915" may need to
> be refactored too.
>
> Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
> Reviewed-by: Prashant Malani <pmalani@chromium.org>
> Signed-off-by: Won Chung <wonchung@google.com>
> ---
>  drivers/misc/mei/hdcp/mei_hdcp.c | 2 +-
>  drivers/misc/mei/pxp/mei_pxp.c   | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/misc/mei/hdcp/mei_hdcp.c b/drivers/misc/mei/hdcp/mei_hdcp.c
> index ec2a4fce8581..e889a8bd7ac8 100644
> --- a/drivers/misc/mei/hdcp/mei_hdcp.c
> +++ b/drivers/misc/mei/hdcp/mei_hdcp.c
> @@ -784,7 +784,7 @@ static int mei_hdcp_component_match(struct device *dev, int subcomponent,
>  {
>         struct device *base = data;
>
> -       if (strcmp(dev->driver->name, "i915") ||
> +       if (!dev->driver || strcmp(dev->driver->name, "i915") ||
>             subcomponent != I915_COMPONENT_HDCP)
>                 return 0;
>
> diff --git a/drivers/misc/mei/pxp/mei_pxp.c b/drivers/misc/mei/pxp/mei_pxp.c
> index f7380d387bab..5c39457e3f53 100644
> --- a/drivers/misc/mei/pxp/mei_pxp.c
> +++ b/drivers/misc/mei/pxp/mei_pxp.c
> @@ -131,7 +131,7 @@ static int mei_pxp_component_match(struct device *dev, int subcomponent,
>  {
>         struct device *base = data;
>
> -       if (strcmp(dev->driver->name, "i915") ||
> +       if (!dev->driver || strcmp(dev->driver->name, "i915") ||
>             subcomponent != I915_COMPONENT_PXP)
>                 return 0;
>
> --
> 2.36.0.rc0.470.gd361397f0d-goog
>

Hi Tomas,

I am adding you to this patch since you are the maintainer of MEI.
If this looks okay to you, could you also take a look at the comment
thread on the cover letter and give an ack if it is okay to be merged
into thunderbolt tree?
https://lore.kernel.org/all/20220418175932.1809770-1-wonchung@google.com/

Thank you,
Won