linux-kernel - Re: [PATCH] drm/amd/display: Add null pointer check for get_first_active

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Message-ID: <36b60ced-932f-4ece-b848-d1b3ffe9e4de@amd.com>
Date: Mon, 26 May 2025 20:42:44 -0600
From: Alex Hung <alex.hung@....com>
To: Wentao Liang <vulab@...as.ac.cn>, harry.wentland@....com,
 sunpeng.li@....com, Rodrigo.Siqueira@....com, alexander.deucher@....com,
 christian.koenig@....com, Xinhui.Pan@....com, crypto@...r.kernel.org,
 airlied@...il.com, simona@...ll.ch
Cc: amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] drm/amd/display: Add null pointer check for
 get_first_active_display()

Reviewed-by: Alex Hung <alex.hung@....com>

On 5/25/25 20:37, Wentao Liang wrote:
> The function mod_hdcp_hdcp1_enable_encryption() calls the function
> get_first_active_display(), but does not check its return value.
> The return value is a null pointer if the display list is empty.
> This will lead to a null pointer dereference in
> mod_hdcp_hdcp2_enable_encryption().
> 
> Add a null pointer check for get_first_active_display() and return
> MOD_HDCP_STATUS_DISPLAY_NOT_FOUND if the function return null.
> 
> Fixes: 2deade5ede56 ("drm/amd/display: Remove hdcp display state with mst fix")
> Cc: stable@...r.kernel.org # v5.8
> Signed-off-by: Wentao Liang <vulab@...as.ac.cn>
> ---
>   drivers/gpu/drm/amd/display/modules/hdcp/hdcp_psp.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/display/modules/hdcp/hdcp_psp.c b/drivers/gpu/drm/amd/display/modules/hdcp/hdcp_psp.c
> index 8c137d7c032e..e58e7b93810b 100644
> --- a/drivers/gpu/drm/amd/display/modules/hdcp/hdcp_psp.c
> +++ b/drivers/gpu/drm/amd/display/modules/hdcp/hdcp_psp.c
> @@ -368,6 +368,9 @@ enum mod_hdcp_status mod_hdcp_hdcp1_enable_encryption(struct mod_hdcp *hdcp)
>   	struct mod_hdcp_display *display = get_first_active_display(hdcp);
>   	enum mod_hdcp_status status = MOD_HDCP_STATUS_SUCCESS;
>   
> +	if (!display)
> +		return MOD_HDCP_STATUS_DISPLAY_NOT_FOUND;
> +
>   	mutex_lock(&psp->hdcp_context.mutex);
>   	hdcp_cmd = (struct ta_hdcp_shared_memory *)psp->hdcp_context.context.mem_context.shared_buf;
>   	memset(hdcp_cmd, 0, sizeof(struct ta_hdcp_shared_memory));