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List:       linux-hardening
Subject:    Re: [PATCH] video: fbdev: au1200fb: replace deprecated strncpy with strscpy
From:       Helge Deller <deller () gmx ! de>
Date:       2024-04-25 9:57:32
Message-ID: 1d6b90c8-1230-4254-9644-1ad56330ab97 () gmx ! de
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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@gmx.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@vger.kernel.org
> > > > > Signed-off-by: Justin Stitt <justinstitt@google.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


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