ACK+cmnt: [SRU Bionic 1/1] UBUNTU: SAUCE: fbdev: remove redundant lock_fb_info

[Thadeu Lima de Souza Cascardo]

On Sat, Sep 24, 2022 at 01:31:25AM +0300, Cengiz Can wrote:
> BugLink: https://bugs.launchpad.net/bugs/1990690
> 
> One of the fixing commits for CVE-2021-33655, commit 159a96b199b4
> ("fbcon: Prevent that screen size is smaller than font size")
> introduced a redundant lock_fb_info line into the ioctl flow in fbmem.c.
> 
> This causes a deadlock when calling FBIOPUT_VSCREENINFO ioctl.
> 
> Remove problematic lock_fb_info call.
> 
> Signed-off-by: Cengiz Can <cengiz.can at canonical.com>

I would just ask to replace "redundant" to something else, like "extraneous",
but this is just nitpicking. As long as the commit messages says explains that
it causes a deadlock, this is fine.

Acked-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>

> ---
>  drivers/video/fbdev/core/fbmem.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> index 1238cc9f42c03..78adcfa11d010 100644
> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -1150,7 +1150,6 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
>  			ret = fb_set_var(info, &var);
>  			info->flags &= ~FBINFO_MISC_USEREVENT;
>  		}
> -		lock_fb_info(info);
>  		unlock_fb_info(info);
>  		console_unlock();
>  		if (!ret && copy_to_user(argp, &var, sizeof(var)))
> -- 
> 2.34.1
> 
> 
> -- 
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