linux-kernel - Re: [PATCH AUTOSEL 6.5 34/52] fbdev: core: cfbcopyarea: fix sloppy typing

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Message-ID: <a93b7be2-a0a6-084d-47e6-a0e8fcd5bc2b@omp.ru>
Date:   Mon, 30 Oct 2023 11:39:14 +0300
From:   Sergey Shtylyov <s.shtylyov@....ru>
To:     Sasha Levin <sashal@...nel.org>, <linux-kernel@...r.kernel.org>,
        <stable@...r.kernel.org>
CC:     Helge Deller <deller@....de>, <daniel@...ll.ch>,
        <linux-fbdev@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH AUTOSEL 6.5 34/52] fbdev: core: cfbcopyarea: fix sloppy
 typing

Hello!

On 10/30/23 1:53 AM, Sasha Levin wrote:

> From: Sergey Shtylyov <s.shtylyov@....ru>
> 
> [ Upstream commit 7f33df94cf0156f64eee9509bd9b4a178990f613 ]
> 
> In cfb_copyarea(), the local variable bits_per_line is needlessly typed as
> *unsigned long* -- which is a 32-bit type on the 32-bit arches and a 64-bit
> type on the 64-bit arches; that variable's value is derived from the __u32
> typed fb_fix_screeninfo::line_length field (multiplied by 8u) and a 32-bit
> *unsigned int* type should still be enough to store the # of bits per line.
> 
> Found by Linux Verification Center (linuxtesting.org) with the Svace static
> analysis tool.
> 
> Signed-off-by: Sergey Shtylyov <s.shtylyov@....ru>
> Signed-off-by: Helge Deller <deller@....de>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  drivers/video/fbdev/core/cfbcopyarea.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/video/fbdev/core/cfbcopyarea.c b/drivers/video/fbdev/core/cfbcopyarea.c
> index 6d4bfeecee350..5b80bf3dae504 100644
> --- a/drivers/video/fbdev/core/cfbcopyarea.c
> +++ b/drivers/video/fbdev/core/cfbcopyarea.c
> @@ -382,7 +382,7 @@ void cfb_copyarea(struct fb_info *p, const struct fb_copyarea *area)
>  {
>  	u32 dx = area->dx, dy = area->dy, sx = area->sx, sy = area->sy;
>  	u32 height = area->height, width = area->width;
> -	unsigned long const bits_per_line = p->fix.line_length*8u;
> +	unsigned int const bits_per_line = p->fix.line_length * 8u;
>  	unsigned long __iomem *base = NULL;
>  	int bits = BITS_PER_LONG, bytes = bits >> 3;
>  	unsigned dst_idx = 0, src_idx = 0, rev_copy = 0;

   I highly doubt this is necessary to pull that into stable. This was
intended to be a cleanup originally.

MBR, Sergey