linux-kernel - Re: [PATCH] usb: typec: fix potential NULL dereference

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Message-ID: <ZD41tLi3sMB71Xf2@kroah.com>
Date:   Tue, 18 Apr 2023 08:16:20 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Maxim Korotkov <korotkov.maxim.s@...il.com>
Cc:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        lvc-project@...uxtesting.org
Subject: Re: [PATCH] usb: typec: fix potential NULL dereference

On Mon, Apr 17, 2023 at 10:50:03PM +0300, Maxim Korotkov wrote:
> The pointer 'adev' was being dereferenced before being checked for NULL
> in the 'type_alt mode_enter()' and 'type_alt mode_exit()' functions.
> Although this is a hypothetical issue, it's better to move the pointer
> assignment after the NULL check to avoid any potential problems.
> 
> Found by Linux Verification Center with Svace static analyzer.
> 
> Fixes: 8a37d87d72f0 ("usb: typec: Bus type for alternate modes")
> Signed-off-by: Maxim Korotkov <korotkov.maxim.s@...il.com>
> ---
>  drivers/usb/typec/bus.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/usb/typec/bus.c b/drivers/usb/typec/bus.c
> index 098f0efaa58d..ae0aca8f33db 100644
> --- a/drivers/usb/typec/bus.c
> +++ b/drivers/usb/typec/bus.c
> @@ -125,13 +125,16 @@ EXPORT_SYMBOL_GPL(typec_altmode_notify);
>   */
>  int typec_altmode_enter(struct typec_altmode *adev, u32 *vdo)
>  {
> -	struct altmode *partner = to_altmode(adev)->partner;
> -	struct typec_altmode *pdev = &partner->adev;
> +	struct altmode *partner;
> +	struct typec_altmode *pdev;
>  	int ret;
>  
>  	if (!adev || adev->active)
>  		return 0;
>  
> +	partner = to_altmode(adev)->partner;
> +	pdev = &partner->adev;

As you point out, the original code is still fine here, we check before
we actually use these values.

Also, can adev every actually be NULL?  In looking at the code paths, I
can't see how that could happen.

thanks,

greg k-h