linux-kernel - Re: truncation in drivers/video/fbdev/neofb.c

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Date:   Tue, 29 Aug 2023 19:11:25 +0200
From:   Helge Deller <deller@....de>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     linux-fbdev@...r.kernel.org,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        clang-built-linux <llvm@...ts.linux.dev>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nathan Chancellor <nathan@...nel.org>
Subject: Re: truncation in drivers/video/fbdev/neofb.c

On 8/29/23 18:45, Nick Desaulniers wrote:
> Helge,
> A recent change in clang made it better about spotting snprintf that
> will result in truncation.  Nathan reported the following instances:
>
> drivers/video/fbdev/neofb.c:1959:3: warning: 'snprintf' will always be
> truncated; specified size is 16, but format string expands to at least
> 17 [-Wfortify-source]
> drivers/video/fbdev/neofb.c:1963:3: warning: 'snprintf' will always be
> truncated; specified size is 16, but format string expands to at least
> 18 [-Wfortify-source]
> drivers/video/fbdev/neofb.c:1967:3: warning: 'snprintf' will always be
> truncated; specified size is 16, but format string expands to at least
> 17 [-Wfortify-source]
> drivers/video/fbdev/neofb.c:1971:3: warning: 'snprintf' will always be
> truncated; specified size is 16, but format string expands to at least
> 17 [-Wfortify-source]
> drivers/video/fbdev/neofb.c:1978:3: warning: 'snprintf' will always be
> truncated; specified size is 16, but format string expands to at least
> 18 [-Wfortify-source]
> drivers/video/fbdev/neofb.c:1985:3: warning: 'snprintf' will always be
> truncated; specified size is 16, but format string expands to at least
> 17 [-Wfortify-source]
> drivers/video/fbdev/neofb.c:1992:3: warning: 'snprintf' will always be
> truncated; specified size is 16, but format string expands to at least
> 18 [-Wfortify-source]
>
> https://github.com/ClangBuiltLinux/linux/issues/1923
>
> Clang is right here.  `info->fix.id` is declared as `char id[16];` so
> indeed string literals like "MagicGraph 256AV+" indeed lead to
> truncation. But this is declared in include/uapi/linux/fb.h; I assume
> those headers cant be changed? Can the strings be shortened then? Is
> it perhaps time to delete this driver?
>
> I see AKPM mentioned alluded to this in
> commit 0e90454 ("neofb: avoid overwriting fb_info fields")
>
> (Also, snprintf probably isn't necessary for string literals that
> don't contain format strings)

It's just an ID field, so I don't think we need the full name of the card.
So using strscpy() and shorten the name, e.g. "MagicGr. 256XL+"
instead of "MagicGraph 256XL+" is probably the most simple solution?

Anyone want to send a patch?

Helge