linux-kernel - Re: [PATCH] drm/i915/display: Fix null pointer dereference in intel_dp_aux_wait_done and intel_dp_aux

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Message-ID: <ZV9ENJIVKztrI2gs@intel.com>
Date:   Thu, 23 Nov 2023 14:23:16 +0200
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Kunwu Chan <chentao@...inos.cn>
Cc:     jani.nikula@...ux.intel.com, joonas.lahtinen@...ux.intel.com,
        rodrigo.vivi@...el.com, tvrtko.ursulin@...ux.intel.com,
        airlied@...il.com, daniel@...ll.ch,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, kunwu.chan@...mail.com
Subject: Re: [PATCH] drm/i915/display: Fix null pointer dereference in
 intel_dp_aux_wait_done and intel_dp_aux_xfer

On Thu, Nov 23, 2023 at 06:04:31PM +0800, Kunwu Chan wrote:
> kasprintf() returns a pointer to dynamically allocated memory
> which can be NULL upon failure. When "intel_dp->aux.name" is NULL,
>  these error messages will trigger the null pointer dereference issue.

How did you reach that conclusion?

> 
> Signed-off-by: Kunwu Chan <chentao@...inos.cn>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_aux.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> index 2e2af71bcd5a..398c9064eb09 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> @@ -67,7 +67,7 @@ intel_dp_aux_wait_done(struct intel_dp *intel_dp)
>  	if (ret == -ETIMEDOUT)
>  		drm_err(&i915->drm,
>  			"%s: did not complete or timeout within %ums (status 0x%08x)\n",
> -			intel_dp->aux.name, timeout_ms, status);
> +			intel_dp->aux.name ? intel_dp->aux.name : "", timeout_ms, status);
>  
>  	return status;
>  }
> @@ -302,7 +302,7 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
>  		if (status != intel_dp->aux_busy_last_status) {
>  			drm_WARN(&i915->drm, 1,
>  				 "%s: not started (status 0x%08x)\n",
> -				 intel_dp->aux.name, status);
> +				 intel_dp->aux.name ? intel_dp->aux.name : "", status);
>  			intel_dp->aux_busy_last_status = status;
>  		}
>  
> @@ -362,7 +362,7 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
>  
>  	if ((status & DP_AUX_CH_CTL_DONE) == 0) {
>  		drm_err(&i915->drm, "%s: not done (status 0x%08x)\n",
> -			intel_dp->aux.name, status);
> +			intel_dp->aux.name ? intel_dp->aux.name : "", status);
>  		ret = -EBUSY;
>  		goto out;
>  	}
> @@ -374,7 +374,7 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
>  	 */
>  	if (status & DP_AUX_CH_CTL_RECEIVE_ERROR) {
>  		drm_err(&i915->drm, "%s: receive error (status 0x%08x)\n",
> -			intel_dp->aux.name, status);
> +			intel_dp->aux.name ? intel_dp->aux.name : "", status);
>  		ret = -EIO;
>  		goto out;
>  	}
> @@ -385,7 +385,7 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
>  	 */
>  	if (status & DP_AUX_CH_CTL_TIME_OUT_ERROR) {
>  		drm_dbg_kms(&i915->drm, "%s: timeout (status 0x%08x)\n",
> -			    intel_dp->aux.name, status);
> +			    intel_dp->aux.name ? intel_dp->aux.name : "", status);
>  		ret = -ETIMEDOUT;
>  		goto out;
>  	}
> @@ -401,7 +401,7 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
>  	if (recv_bytes == 0 || recv_bytes > 20) {
>  		drm_dbg_kms(&i915->drm,
>  			    "%s: Forbidden recv_bytes = %d on aux transaction\n",
> -			    intel_dp->aux.name, recv_bytes);
> +			    intel_dp->aux.name ? intel_dp->aux.name : "", recv_bytes);
>  		ret = -EBUSY;
>  		goto out;
>  	}
> -- 
> 2.34.1

-- 
Ville Syrjälä
Intel