linux-kernel - Re: [PATCH v2] usb: typec: ucsi: Fix NULL pointer dereference in ucsi_displayport

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Message-ID: <pva5d2tl2zxeaugahq7rih6o2w64pr5kuu2yyhdvcb264t3uyf@42whgfttylzb>
Date: Tue, 23 Jul 2024 17:21:20 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Ma Ke <make24@...as.ac.cn>
Cc: heikki.krogerus@...ux.intel.com, gregkh@...uxfoundation.org, 
	utkarsh.h.patel@...el.com, abhishekpandit@...omium.org, andriy.shevchenko@...ux.intel.com, 
	kyletso@...gle.com, linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org, 
	stable@...r.kernel.org
Subject: Re: [PATCH v2] usb: typec: ucsi: Fix NULL pointer dereference in
 ucsi_displayport_vdm()

On Tue, Jul 23, 2024 at 10:13:44PM GMT, Ma Ke wrote:
> When dp->con->partner is an error, a NULL pointer dereference may occur.
> Add a check for dp->con->partner to avoid dereferencing a NULL pointer.
> 
> Cc: stable@...r.kernel.org
> Fixes: 372adf075a43 ("usb: typec: ucsi: Determine common SVDM Version")
> Signed-off-by: Ma Ke <make24@...as.ac.cn>
> ---
> Changes in v2:
> - added Cc stable line;
> - fixed a typo.
> ---
>  drivers/usb/typec/ucsi/displayport.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/usb/typec/ucsi/displayport.c b/drivers/usb/typec/ucsi/displayport.c
> index 420af5139c70..ecc706e0800d 100644
> --- a/drivers/usb/typec/ucsi/displayport.c
> +++ b/drivers/usb/typec/ucsi/displayport.c
> @@ -222,6 +222,8 @@ static int ucsi_displayport_vdm(struct typec_altmode *alt,
>  	switch (cmd_type) {
>  	case CMDT_INIT:
>  		if (PD_VDO_SVDM_VER(header) < svdm_version) {
> +			if (IS_ERR_OR_NULL(dp->con->partner))

Usually IS_ERR_OR_NULL is one of the red flags. It is either IS_ERR or
NULL, but not both.

Also could you please describe the path how we can end up here without a
proper dp->con->partner.

> +				break;
>  			typec_partner_set_svdm_version(dp->con->partner, PD_VDO_SVDM_VER(header));
>  			svdm_version = PD_VDO_SVDM_VER(header);
>  		}
> -- 
> 2.25.1
> 

-- 
With best wishes
Dmitry