linux-kernel - Re: [PATCH 1/5] drm/modes: parse_cmdline: Handle empty mode name part

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Date:   Fri, 8 Jul 2022 21:28:32 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-m68k@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] drm/modes: parse_cmdline: Handle empty mode name part

Hi Geert,

On 7/8/22 20:21, Geert Uytterhoeven wrote:
> If no mode name part was specified, mode_end is zero, and the "ret ==
> mode_end" check does the wrong thing.
> 
> Fix this by checking for a non-zero return value instead.

Which is wrong to do, since now if you have e.g. a mode list
with:

"dblntsc",
"dblntsc-ff"

in there and the cmdline contains "dblntsc-ff" then you
will already stop with a (wrong!) match at "dblntsc".

> While at it, skip all named mode handling when mode_end is zero, as it
> is futile.

AFAICT, this is actually what needs to be done to fix this, while keeping
the ret == mode_end check.

Regards,

Hans


> 
> Fixes: 7b1cce760afe38b4 ("drm/modes: parse_cmdline: Allow specifying stand-alone options")
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> ---
>  drivers/gpu/drm/drm_modes.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> index 14b746f7ba975954..30a7be97707bfb16 100644
> --- a/drivers/gpu/drm/drm_modes.c
> +++ b/drivers/gpu/drm/drm_modes.c
> @@ -1823,9 +1823,9 @@ bool drm_mode_parse_command_line_for_connector(const char *mode_option,
>  	}
>  
>  	/* First check for a named mode */
> -	for (i = 0; i < ARRAY_SIZE(drm_named_modes_whitelist); i++) {
> +	for (i = 0; mode_end && i < ARRAY_SIZE(drm_named_modes_whitelist); i++) {
>  		ret = str_has_prefix(name, drm_named_modes_whitelist[i]);
> -		if (ret == mode_end) {
> +		if (ret) {
>  			if (refresh_ptr)
>  				return false; /* named + refresh is invalid */
>