Message-ID: <2026011541-froth-cabdriver-a214@gregkh>
Date: Thu, 15 Jan 2026 07:32:04 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: 齐柯宇 <qikeyu2017@...il.com>
Cc: heikki.krogerus@...ux.intel.com, andersson@...nel.org,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: typec: mux: fix NULL pointer dereference in
 {typec_switch,mux}_put

On Thu, Jan 15, 2026 at 02:56:24AM +0800, 齐柯宇 wrote:
> This fix was discovered through static code analysis.
> 
> In typec_switch_put() and typec_mux_put(), the code directly dereferences
> sw_dev->dev.parent->driver->owner without checking if 'driver' is NULL.
> This can lead to a NULL pointer dereference kernel crash.
> 
> [Call Chain Analysis]
> The vulnerable functions are called through the following paths:
> 
>   Acquisition path (fwnode_typec_switch_get):
>     typec_port_register()           [class.c]
>       -> typec_switch_get()         [typec_mux.h]
>         -> fwnode_typec_switch_get() [mux.c]
>           -> class_find_device()    (gets device reference)
>           -> try_module_get(sw_devs[i]->dev.parent->driver->owner)
>           -> stores to sw->sw_devs[i]
> 
>   Release path (typec_switch_put):
>     typec_release()                 [class.c]
>       -> typec_switch_put()         [mux.c]
>         -> module_put(sw_dev->dev.parent->driver->owner)  <- BUG!
>         -> put_device(&sw_dev->dev)
> 
>   Registration path (typec_switch_register):
>     I2C/Platform driver probe()
>       -> typec_switch_register(dev, &sw_desc) [mux.c]
>         -> sw_dev->dev.parent = parent  (sets parent device)
>         -> device_add(&sw_dev->dev)
> 
> [Data Flow Analysis]
> The critical data flow is:
> 
>   sw_dev->dev.parent:
>     - Set by typec_switch_register() from the 'parent' parameter
>     - Typically an I2C or Platform device (e.g., &client->dev)
> 
>   sw_dev->dev.parent->driver:
>     - Managed by kernel driver model (drivers/base/dd.c)
>     - Set to driver pointer when driver binds (really_probe)
>     - Set to NULL when driver unbinds (__device_release_driver)
> 
> [Race Condition Scenario]
> The vulnerability can be triggered by the following race condition:
> 
>   Thread A (normal operation)        Thread B (attacker/event)
>   ----------------------------       -------------------------
>   T1: typec_port_register()
>   T2: fwnode_typec_switch_get()
>   T3: try_module_get(parent->driver->owner)
>   T4: store sw_devs[i]
>       ...
>                                      T5: echo <dev> > unbind
>                                      T6: device_driver_detach()
>                                      T7: parent->driver = NULL
>   T8: typec_switch_put(sw)
>   T9: module_put(parent->driver->owner)
>       -> NULL pointer dereference!
> 
> [User-Triggerable Paths]
> Users can trigger this vulnerability through:
> 
>   1. sysfs unbind interface (requires root):
>      # echo "<device>" > /sys/bus/i2c/drivers/<driver>/unbind
> 
>   2. Module unloading (requires root):
>      # rmmod <switch_driver_module>
> 
>   3. USB Type-C hot-unplug (physical access):
>      Physically removing the USB-C device or its parent device
> 
> How to fix:
> Add NULL checks for both 'parent' and 'parent->driver' before calling
> module_put() in typec_switch_put() and typec_mux_put().
> 
> Fixes: 71793b579ba68 ("usb: typec: mux: Allow multiple mux_devs per mux")
> Signed-off-by: Kery Qi <qikeyu2017@...il.com>
> ---
>  drivers/usb/typec/mux.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/typec/mux.c b/drivers/usb/typec/mux.c
> index 182c902c42f6..6ed8bb999ee0 100644
> --- a/drivers/usb/typec/mux.c
> +++ b/drivers/usb/typec/mux.c
> @@ -134,7 +134,8 @@ void typec_switch_put(struct typec_switch *sw)
>   for (i = 0; i < sw->num_sw_devs; i++) {
>     sw_dev = sw->sw_devs[i];
> 
> -   module_put(sw_dev->dev.parent->driver->owner);
> +   if (sw_dev->dev.parent && sw_dev->dev.parent->driver)
> +     module_put(sw_dev->dev.parent->driver->owner);
>     put_device(&sw_dev->dev);
>   }
>   kfree(sw);
> @@ -358,7 +359,8 @@ void typec_mux_put(struct typec_mux *mux)
> 
>   for (i = 0; i < mux->num_mux_devs; i++) {
>     mux_dev = mux->mux_devs[i];
> -   module_put(mux_dev->dev.parent->driver->owner);
> +   if (mux_dev->dev.parent && mux_dev->dev.parent->driver)
> +     module_put(mux_dev->dev.parent->driver->owner);
>     put_device(&mux_dev->dev);
>   }
>   kfree(mux);
> -- 
> 2.34.1
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
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If you wish to discuss this problem further, or you have questions about
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thanks,

greg k-h's patch email bot

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