[PATCH 1/2] video: fbdev: core: cfbcopyarea: fix sloppy typing

[Helge Deller]

On 9/18/23 22:52, Sergey Shtylyov wrote:
> In cfb_copyarea(), when initializing *unsigned long const* bits_per_line
> __u32 typed fb_fix_screeninfo::line_length gets multiplied by 8u -- which
> might overflow __u32; multiplying by 8UL instead should fix that...
> Also, that bits_per_line constant is used to advance *unsigned* src_idx
> and dst_idx variables -- which might be overflowed as well; declaring
> them as *unsigned long* should fix that too...
>
> Found by Linux Verification Center (linuxtesting.org) with the Svace static
> analysis tool.
>
> Signed-off-by: Sergey Shtylyov <s.shtylyov at omp.ru>
> Cc: stable at vger.kernel.org
> ---
>   drivers/video/fbdev/core/cfbcopyarea.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/video/fbdev/core/cfbcopyarea.c b/drivers/video/fbdev/core/cfbcopyarea.c
> index 6d4bfeecee35..b67ba69ea2fb 100644
> --- a/drivers/video/fbdev/core/cfbcopyarea.c
> +++ b/drivers/video/fbdev/core/cfbcopyarea.c
> @@ -382,10 +382,11 @@ 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 long const bits_per_line = p->fix.line_length * 8UL;

you wrote:
> __u32 typed fb_fix_screeninfo::line_length gets multiplied by 8u -- which
> might overflow __u32; multiplying by 8UL instead should fix that...

This would only be true on 64-bit CPUs, where unsigned long is 64 bits,
while on 32-bit CPUs, it's still 32 bits (same as _u32).

Instead we could make bits_per_line __u32 (or unsigned int) too.

>   	unsigned long __iomem *base = NULL;
>   	int bits = BITS_PER_LONG, bytes = bits >> 3;
> -	unsigned dst_idx = 0, src_idx = 0, rev_copy = 0;
> +	unsigned long dst_idx = 0, src_idx = 0;

An "unsigned int" can address at least up to 4GB, which is fully sufficent here.

So, both patches don't have any real effect.
NAK.

Helge