linux-kernel - Re: [PATCH 1/2] drm: Use size_t type for len variable in drm_copy

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Message-ID: <7ae9ae81-f99f-adc4-85be-a6ac9ad9b72f@suse.de>
Date:   Mon, 4 Jul 2022 14:27:23 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Javier Martinez Canillas <javierm@...hat.com>,
        linux-kernel@...r.kernel.org
Cc:     Peter Robinson <pbrobinson@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 1/2] drm: Use size_t type for len variable in
 drm_copy_field()



Am 01.07.22 um 14:07 schrieb Javier Martinez Canillas:
> The strlen() function returns a size_t which is an unsigned int on 32-bit
> arches and an unsigned long on 64-bit arches. But in the drm_copy_field()
> function, the strlen() return value is assigned to an 'int len' variable.
> 
> Later, the len variable is passed as copy_from_user() third argument that
> is an unsigned long parameter as well.
> 
> In theory, this can lead to an integer overflow via type conversion. Since
> the assignment happens to a signed int lvalue instead of a size_t lvalue.
> 
> In practice though, that's unlikely since the values copied are set by DRM
> drivers and not controlled by userspace. But using a size_t for len is the
> correct thing to do anyways.
> 
> Reported-by: Peter Robinson <pbrobinson@...il.com>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>

Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>

> ---
> 
>   drivers/gpu/drm/drm_ioctl.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
> index 8faad23dc1d8..e1b9a03e619c 100644
> --- a/drivers/gpu/drm/drm_ioctl.c
> +++ b/drivers/gpu/drm/drm_ioctl.c
> @@ -472,7 +472,7 @@ EXPORT_SYMBOL(drm_invalid_op);
>    */
>   static int drm_copy_field(char __user *buf, size_t *buf_len, const char *value)
>   {
> -	int len;
> +	size_t len;
>   
>   	/* don't overflow userbuf */
>   	len = strlen(value);

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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