linux-kernel - Re: [PATCH RESEND] drm/stm: ltdc: fix late dereference check

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Date:   Fri, 26 May 2023 13:40:41 +0200
From:   Philippe CORNU <philippe.cornu@...s.st.com>
To:     Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>,
        Yannick Fertre <yannick.fertre@...s.st.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>
CC:     <dri-devel@...ts.freedesktop.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, kernel test robot <lkp@...el.com>,
        Dan Carpenter <error27@...il.com>
Subject: Re: [PATCH RESEND] drm/stm: ltdc: fix late dereference check


On 5/15/23 14:38, Raphael Gallais-Pou wrote:
> In ltdc_crtc_set_crc_source(), struct drm_crtc was dereferenced in a
> container_of() before the pointer check. This could cause a kernel panic.
> 
> Fix this smatch warning:
> drivers/gpu/drm/stm/ltdc.c:1124 ltdc_crtc_set_crc_source() warn: variable dereferenced before check 'crtc' (see line 1119)
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Reported-by: Dan Carpenter <error27@...il.com>
> Link: https://lore.kernel.org/lkml/202212241802.zeLFZCXB-lkp@intel.com/
> Signed-off-by: Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>
> ---
>   drivers/gpu/drm/stm/ltdc.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
> index 03c6becda795..b8be4c1db423 100644
> --- a/drivers/gpu/drm/stm/ltdc.c
> +++ b/drivers/gpu/drm/stm/ltdc.c
> @@ -1145,7 +1145,7 @@ static void ltdc_crtc_disable_vblank(struct drm_crtc *crtc)
>   
>   static int ltdc_crtc_set_crc_source(struct drm_crtc *crtc, const char *source)
>   {
> -	struct ltdc_device *ldev = crtc_to_ltdc(crtc);
> +	struct ltdc_device *ldev;
>   	int ret;
>   
>   	DRM_DEBUG_DRIVER("\n");
> @@ -1153,6 +1153,8 @@ static int ltdc_crtc_set_crc_source(struct drm_crtc *crtc, const char *source)
>   	if (!crtc)
>   		return -ENODEV;
>   
> +	ldev = crtc_to_ltdc(crtc);
> +
>   	if (source && strcmp(source, "auto") == 0) {
>   		ldev->crc_active = true;
>   		ret = regmap_set_bits(ldev->regmap, LTDC_GCR, GCR_CRCEN);

Hi Raphael,
Applied on drm-misc-next.

Note & fyi, I fixed the following warning, please be sure to follow this 
rule next time :-)
WARNING:BAD_REPORTED_BY_LINK: Reported-by: should be immediately 
followed by Closes: with a URL to the report

Many thanks for your patch,
Philippe :-)