linux-hardening - Re: [PATCH] video: fbdev: au1200fb: replace deprecated strncpy with strscpy

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Date: Thu, 25 Apr 2024 12:00:02 +0200
From: Helge Deller <deller@....de>
To: Kees Cook <keescook@...omium.org>
Cc: Justin Stitt <justinstitt@...gle.com>, linux-fbdev@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH] video: fbdev: au1200fb: replace deprecated strncpy with
 strscpy

On 4/25/24 01:49, Kees Cook wrote:
> On Wed, Mar 20, 2024 at 11:48:52PM +0100, Helge Deller wrote:
>> On 3/20/24 23:35, Justin Stitt wrote:
>>> Hi,
>>>
>>> On Wed, Mar 20, 2024 at 12:56 AM Helge Deller <deller@....de> wrote:
>>>>
>>>> On 3/19/24 00:46, Justin Stitt wrote:
>>>>> strncpy() is deprecated for use on NUL-terminated destination strings
>>>>> [1] and as such we should prefer more robust and less ambiguous string
>>>>> interfaces.
>>>>>
>>>>> Let's use the new 2-argument strscpy() which guarantees NUL-termination
>>>>> on the destination buffer while also simplifying the syntax. Note that
>>>>> strscpy() will not NUL-pad the destination buffer like strncpy() does.
>>>>>
>>>>> However, the NUL-padding behavior of strncpy() is not required since
>>>>> fbdev is already NUL-allocated from au1200fb_drv_probe() ->
>>>>> frameuffer_alloc(), rendering any additional NUL-padding redundant.
>>>>> |     p = kzalloc(fb_info_size + size, GFP_KERNEL);
>>>>>
>>>>> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
>>>>> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
>>>>> Link: https://github.com/KSPP/linux/issues/90
>>>>> Cc: linux-hardening@...r.kernel.org
>>>>> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
>>>>> ---
>>>>> Note: build-tested only.
>>>>>
>>>>> Found with: $ rg "strncpy\("
>>>>> ---
>>>>>     drivers/video/fbdev/au1200fb.c | 2 +-
>>>>>     1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/video/fbdev/au1200fb.c b/drivers/video/fbdev/au1200fb.c
>>>>> index 6f20efc663d7..e718fea63662 100644
>>>>> --- a/drivers/video/fbdev/au1200fb.c
>>>>> +++ b/drivers/video/fbdev/au1200fb.c
>>>>> @@ -1557,7 +1557,7 @@ static int au1200fb_init_fbinfo(struct au1200fb_device *fbdev)
>>>>>                 return ret;
>>>>>         }
>>>>>
>>>>> -     strncpy(fbi->fix.id, "AU1200", sizeof(fbi->fix.id));
>>>>> +     strscpy(fbi->fix.id, "AU1200");
>>>>
>>>> I wonder if you really build-tested this, as this driver is for the mips architecture...
>>>> And I don't see a strscpy() function which takes just 2 arguments.
>>>> But I might be wrong....
>>>
>>> I did build successfully :thumbs_up:
>>>
>>> Commit e6584c3964f2f ("string: Allow 2-argument strscpy()") introduced
>>> this new strscpy() form; it is present in string.h on Linus' tree.
>>
>> Interesting patch.
>> Might give compile problems if patches like yours gets automatically
>> picked up to stable series as long as Kees patch hasn't been backported yet...
>> Anyway, thanks for the pointer!
>> I'll apply your patch in the next round for fbdev.
>
> Hi! I haven't seen this show up in -next yet. Have you had a chance to
> pick it up?
>
> There are also these too:
>
> https://lore.kernel.org/all/20240320-strncpy-drivers-video-fbdev-fsl-diu-fb-c-v1-1-3cd3c012fa8c@google.com/
> https://patchwork.kernel.org/project/linux-hardening/patch/20240320-strncpy-drivers-video-fbdev-uvesafb-c-v1-1-fd6af3766c80@google.com/
> https://patchwork.kernel.org/project/linux-hardening/patch/20240320-strncpy-drivers-video-hdmi-c-v1-1-f9a08168cdaf@google.com/

All 4 patches picked up into fbdev for-next git tree now.

Thanks!
Helge