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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Thu, 31 Aug 2023 15:26:35 -0700
Message-ID: <CAKwvOdkqZwF_HqyPhm3hxOVpsWqhN4X=bwUw66=ZkPSpwGpLAA@mail.gmail.com>
Subject: Re: truncation in drivers/video/fbdev/neofb.c
To:     Helge Deller <deller@gmx.de>
Cc:     linux-fbdev@vger.kernel.org,
        dri-devel <dri-devel@lists.freedesktop.org>,
        clang-built-linux <llvm@lists.linux.dev>,
        LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Justin Stitt <justinstitt@google.com>
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On Thu, Aug 31, 2023 at 3:16=E2=80=AFPM Helge Deller <deller@gmx.de> wrote:
>
> * Nick Desaulniers <ndesaulniers@google.com>:
> > On Thu, Aug 31, 2023 at 2:23=E2=80=AFPM Helge Deller <deller@gmx.de> wr=
ote:
> > >
> > > * Helge Deller <deller@gmx.de>:
> > > > On 8/29/23 18:45, Nick Desaulniers wrote:
> > > > > A recent change in clang made it better about spotting snprintf t=
hat
> > > > > will result in truncation.  Nathan reported the following instanc=
es:
> > > > >
> > > > > drivers/video/fbdev/neofb.c:1959:3: warning: 'snprintf' will alwa=
ys be
> > > > > truncated; specified size is 16, but format string expands to at =
least
> > > > > 17 [-Wfortify-source]
> > >
> > > FYI, I've added the patch below to the fbdev for-next git tree.
> > > [...]
> >
> > This indeed makes the warning go away, but that's more so due to the
> > use of strscpy now rather than snprintf.  That alone is a good change
> > but we still have definite truncation.  See below:
> > [...]
>
> Nick, thanks for your review and findings!
> Now every string should be max. 15 chars (which fits with the trailing
> NUL into the char[16] array).
>
> Helge
>
>
> Subject: [PATCH] fbdev: neofb: Shorten Neomagic product name in info stru=
ct
>
> Avoid those compiler warnings:
> neofb.c:1959:3: warning: 'snprintf' will always be truncated;
>    specified size is 16, but format string expands to at least 17 [-Wfort=
ify-source]
>
> Signed-off-by: Helge Deller <deller@gmx.de>
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Reported-by: Nick Desaulniers <ndesaulniers@google.com>
> Link: https://lore.kernel.org/all/CAKwvOdn0xoVWjQ6ufM_rojtKb0f1i1hW-J_xYG=
fKDNFdHwaeHQ@mail.gmail.com/
> Link: https://github.com/ClangBuiltLinux/linux/issues/1923

ah yeah LGTM

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

>
> diff --git a/drivers/video/fbdev/neofb.c b/drivers/video/fbdev/neofb.c
> index d2f622b4c372..b58b11015c0c 100644
> --- a/drivers/video/fbdev/neofb.c
> +++ b/drivers/video/fbdev/neofb.c
> @@ -1948,49 +1948,40 @@ static struct fb_info *neo_alloc_fb_info(struct p=
ci_dev *dev,
>
>         switch (info->fix.accel) {
>         case FB_ACCEL_NEOMAGIC_NM2070:
> -               snprintf(info->fix.id, sizeof(info->fix.id),
> -                               "MagicGraph 128");
> +               strscpy(info->fix.id, "MagicGraph128", sizeof(info->fix.i=
d));
>                 break;
>         case FB_ACCEL_NEOMAGIC_NM2090:
> -               snprintf(info->fix.id, sizeof(info->fix.id),
> -                               "MagicGraph 128V");
> +               strscpy(info->fix.id, "MagicGraph128V", sizeof(info->fix.=
id));
>                 break;
>         case FB_ACCEL_NEOMAGIC_NM2093:
> -               snprintf(info->fix.id, sizeof(info->fix.id),
> -                               "MagicGraph 128ZV");
> +               strscpy(info->fix.id, "MagicGraph128ZV", sizeof(info->fix=
.id));
>                 break;
>         case FB_ACCEL_NEOMAGIC_NM2097:
> -               snprintf(info->fix.id, sizeof(info->fix.id),
> -                               "MagicGraph 128ZV+");
> +               strscpy(info->fix.id, "Mag.Graph128ZV+", sizeof(info->fix=
.id));
>                 break;
>         case FB_ACCEL_NEOMAGIC_NM2160:
> -               snprintf(info->fix.id, sizeof(info->fix.id),
> -                               "MagicGraph 128XD");
> +               strscpy(info->fix.id, "MagicGraph128XD", sizeof(info->fix=
.id));
>                 break;
>         case FB_ACCEL_NEOMAGIC_NM2200:
> -               snprintf(info->fix.id, sizeof(info->fix.id),
> -                               "MagicGraph 256AV");
> +               strscpy(info->fix.id, "MagicGraph256AV", sizeof(info->fix=
.id));
>                 info->flags |=3D FBINFO_HWACCEL_IMAGEBLIT |
>                                FBINFO_HWACCEL_COPYAREA |
>                                FBINFO_HWACCEL_FILLRECT;
>                 break;
>         case FB_ACCEL_NEOMAGIC_NM2230:
> -               snprintf(info->fix.id, sizeof(info->fix.id),
> -                               "MagicGraph 256AV+");
> +               strscpy(info->fix.id, "Mag.Graph256AV+", sizeof(info->fix=
.id));
>                 info->flags |=3D FBINFO_HWACCEL_IMAGEBLIT |
>                                FBINFO_HWACCEL_COPYAREA |
>                                FBINFO_HWACCEL_FILLRECT;
>                 break;
>         case FB_ACCEL_NEOMAGIC_NM2360:
> -               snprintf(info->fix.id, sizeof(info->fix.id),
> -                               "MagicGraph 256ZX");
> +               strscpy(info->fix.id, "MagicGraph256ZX", sizeof(info->fix=
.id));
>                 info->flags |=3D FBINFO_HWACCEL_IMAGEBLIT |
>                                FBINFO_HWACCEL_COPYAREA |
>                                FBINFO_HWACCEL_FILLRECT;
>                 break;
>         case FB_ACCEL_NEOMAGIC_NM2380:
> -               snprintf(info->fix.id, sizeof(info->fix.id),
> -                               "MagicGraph 256XL+");
> +               strscpy(info->fix.id, "Mag.Graph256XL+", sizeof(info->fix=
.id));
>                 info->flags |=3D FBINFO_HWACCEL_IMAGEBLIT |
>                                FBINFO_HWACCEL_COPYAREA |
>                                FBINFO_HWACCEL_FILLRECT;
>


--=20
Thanks,
~Nick Desaulniers