linux-kernel - Re: [PATCH][next] drm/gud: Use size_add() in call to struct

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Message-ID: <202309151150.74DBDCA039@keescook>
Date:   Fri, 15 Sep 2023 11:52:02 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Noralf Trønnes <noralf@...nnes.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, Peter Stuge <peter@...ge.se>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] drm/gud: Use size_add() in call to struct_size()

On Fri, Sep 15, 2023 at 12:43:20PM -0600, Gustavo A. R. Silva wrote:
> If, for any reason, the open-coded arithmetic causes a wraparound, the
> protection that `struct_size()` adds against potential integer overflows
> is defeated. Fix this by hardening call to `struct_size()` with `size_add()`.
> 
> Fixes: 40e1a70b4aed ("drm: Add GUD USB Display driver")
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>  drivers/gpu/drm/gud/gud_pipe.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/gud/gud_pipe.c b/drivers/gpu/drm/gud/gud_pipe.c
> index d2f199ea3c11..a02f75be81f0 100644
> --- a/drivers/gpu/drm/gud/gud_pipe.c
> +++ b/drivers/gpu/drm/gud/gud_pipe.c
> @@ -503,7 +503,7 @@ int gud_pipe_check(struct drm_simple_display_pipe *pipe,
>  		return -ENOENT;
>  
>  	len = struct_size(req, properties,
> -			  GUD_PROPERTIES_MAX_NUM + GUD_CONNECTOR_PROPERTIES_MAX_NUM);
> +			  size_add(GUD_PROPERTIES_MAX_NUM, GUD_CONNECTOR_PROPERTIES_MAX_NUM));

There are both constant expressions, so there's not too much value in
wrapping them with size_add(), but for maintaining a common coding style
for dealing with allocation sizes, I can be convinced of the change. :)

Reviewed-by: Kees Cook <keescook@...omium.org>


>  	req = kzalloc(len, GFP_KERNEL);
>  	if (!req)
>  		return -ENOMEM;
> -- 
> 2.34.1
> 

-- 
Kees Cook