Message-ID: <edcf26d4-64a0-04ea-435c-17d9efde7dd9@kernel.org>
Date:   Thu, 26 Jan 2023 10:08:07 +0100
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Subject: Re: [PATCH] fbcon: Check font dimension limits
Content-Language: en-US
To:     Greg KH <gregkh@linuxfoundation.org>,
        Samuel Thibault <samuel.thibault@ens-lyon.org>
Cc:     Daniel Vetter <daniel@ffwll.ch>, Helge Deller <deller@gmx.de>,
        linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Sanan Hasanov <sanan.hasanov@knights.ucf.edu>
References: <20230126004911.869923511@ens-lyon.org>
 <20230126004921.616264824@ens-lyon.org> <Y9IvBoAbmh27xl4B@kroah.com>
From:   Jiri Slaby <jirislaby@kernel.org>
In-Reply-To: <Y9IvBoAbmh27xl4B@kroah.com>
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Precedence: bulk

On 26. 01. 23, 8:43, Greg KH wrote:
>> --- linux-6.0.orig/drivers/video/fbdev/core/fbcon.c
>> +++ linux-6.0/drivers/video/fbdev/core/fbcon.c
>> @@ -2489,9 +2489,12 @@ static int fbcon_set_font(struct vc_data
>>   	    h > FBCON_SWAP(info->var.rotate, info->var.yres, info->var.xres))
>>   		return -EINVAL;
>>   
>> +	if (font->width > 32 || font->height > 32)
>> +		return -EINVAL;
>> +
>>   	/* Make sure drawing engine can handle the font */
>> -	if (!(info->pixmap.blit_x & (1 << (font->width - 1))) ||
>> -	    !(info->pixmap.blit_y & (1 << (font->height - 1))))
>> +	if (!(info->pixmap.blit_x & (1U << (font->width - 1))) ||
>> +	    !(info->pixmap.blit_y & (1U << (font->height - 1))))
> 
> Are you sure this is still needed with the above check added?  If so,
> why?  What is the difference in the compiled code?

For font->{width,height} == 32, definitely. IMO, 1 << 31 is undefined as 
1 << 31 cannot be represented by an (signed) int.

-- 
js
suse labs