linux-kernel - Re: [PATCH v2] fbdev: bitblit: bound-check glyph index in bit

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Message-ID: <5b5ec5ea-7a81-457c-9ab1-6c56a722c5e5@gmx.de>
Date: Tue, 28 Oct 2025 22:23:59 +0100
From: Helge Deller <deller@....de>
To: linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] fbdev: bitblit: bound-check glyph index in bit_putcs*

On 10/20/25 16:29, Thomas Zimmermann wrote:
> Hi
> 
> Am 20.10.25 um 15:47 schrieb Junjie Cao:
>> bit_putcs_aligned()/unaligned() derived the glyph pointer from the
>> character value masked by 0xff/0x1ff, which may exceed the actual font's
>> glyph count and read past the end of the built-in font array.
>> Clamp the index to the actual glyph count before computing the address.
>>
>> This fixes a global out-of-bounds read reported by syzbot.
>>
>> Reported-by: syzbot+793cf822d213be1a74f2@...kaller.appspotmail.com
>> Closes: https://syzkaller.appspot.com/bug?extid=793cf822d213be1a74f2
>> Tested-by: syzbot+793cf822d213be1a74f2@...kaller.appspotmail.com
>> Signed-off-by: Junjie Cao <junjie.cao@...el.com>
> 
> Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>
...
>> v1: https://lore.kernel.org/linux-fbdev/5d237d1a-a528-4205-a4d8-71709134f1e1@suse.de/
>> v1 -> v2:
>>   - Fix indentation and add blank line after declarations with the .pl helper
>>   - No functional changes
>>
>>   drivers/video/fbdev/core/bitblit.c | 16 ++++++++++++----
>>   1 file changed, 12 insertions(+), 4 deletions(-)

applied.

Thanks!
Helge