linux-kernel - Re: [PATCH] drm/modes: Fix unterminated strncpy

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Message-ID: <20190730171227.GS104440@art_vandelay>
Date:   Tue, 30 Jul 2019 13:12:27 -0400
From:   Sean Paul <sean@...rly.run>
To:     Chuhong Yuan <hslester96@...il.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/modes: Fix unterminated strncpy

On Tue, Jul 30, 2019 at 04:40:32PM +0800, Chuhong Yuan wrote:
> strncpy(dest, src, strlen(src)) leads to unterminated
> dest, which is dangerous.
> Fix it by using strscpy.
> 
> Signed-off-by: Chuhong Yuan <hslester96@...il.com>
> ---
>  drivers/gpu/drm/drm_modes.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> index 80fcd5dc1558..170fc24e0f31 100644
> --- a/drivers/gpu/drm/drm_modes.c
> +++ b/drivers/gpu/drm/drm_modes.c
> @@ -1770,7 +1770,7 @@ bool drm_mode_parse_command_line_for_connector(const char *mode_option,
>  	}
>  
>  	if (named_mode) {
> -		strncpy(mode->name, name, mode_end);
> +		strscpy(mode->name, name, mode_end + 1);

Shouldn't you be checking that mode_end + 1 is not > than the size of mode->name
(ie: DRM_DISPLAY_MODE_LEN)? This still seems unsafe.

Sean

>  	} else {
>  		ret = drm_mode_parse_cmdline_res_mode(name, mode_end,
>  						      parse_extras,
> -- 
> 2.20.1
> 

-- 
Sean Paul, Software Engineer, Google / Chromium OS