linux-kernel - Re: [PATCH v3] misc/mei: Add NULL check to component match callback functions

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Date:   Thu, 31 Mar 2022 11:00:46 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Won Chung <wonchung@...gle.com>
Cc:     Tomas Winkler <tomas.winkler@...el.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Benson Leung <bleung@...omium.org>,
        Prashant Malani <pmalani@...omium.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v3] misc/mei: Add NULL check to component match callback
 functions

On Thu, Mar 31, 2022 at 08:49:18AM +0000, Won Chung wrote:
> Component match callback functions need to check if expected data is
> passed to them. Without this check, it can cause a NULL pointer
> dereference when another driver registers a component before i915
> drivers have their component master fully bind.

How can that happen in a real system?  Or does this just happen for when
you are doing development and testing?

> 
> Fixes: 1e8d19d9b0dfc ("mei: hdcp: bind only with i915 on the same PCH")
> Fixes: c2004ce99ed73 ("mei: pxp: export pavp client to me client bus")
> Suggested-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> Suggested-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> Signed-off-by: Won Chung <wonchung@...gle.com>
> Cc: stable@...r.kernel.org

Why does this need to go to stable?  How can this be triggered in older
kernels?

> ---
> Changes from v2:
> - Correctly add "Suggested-by" tag
> - Add "Cc: stable@...r.kernel.org"
> 
> Changes from v1:
> - Add "Fixes" tag
> - Send to stable@...r.kernel.org
> 
>  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..843dbc2b21b1 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 (!base || !dev->driver || strcmp(dev->driver->name, "i915") ||

How can base be NULL?


>  	    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..e32a81da8af6 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 (!base || !dev->driver || strcmp(dev->driver->name, "i915") ||

Same here, shouldn't this be caught by the driver core or bus and match
should not be called?

Why not fix this in the component/driver core instead?

thanks,

greg k-h