linux-kernel - Re: [PATCH v3] lib/string.c: implement stpcpy

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Message-ID: <CAHp75VeA6asim81CwxPD7LKc--DEvOWH9fwgQ9Bbb1Xf55OYKw@mail.gmail.com>
Date:   Thu, 27 Aug 2020 23:05:42 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Joe Perches <joe@...ches.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        stable <stable@...r.kernel.org>, Andy Lavr <andy.lavr@...il.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Alexandru Ardelean <alexandru.ardelean@...log.com>,
        Yury Norov <yury.norov@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] lib/string.c: implement stpcpy

On Thu, Aug 27, 2020 at 9:30 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Thu, Aug 27, 2020 at 11:59:24AM +0300, Andy Shevchenko wrote:
> > strcpy() is not a bad API for the cases when you know what you are
> > doing. A problem that most of the developers do not know what they are
> > doing.
> > No need to split everything to bad and good by its name or semantics,
> > each API has its own pros and cons and programmers must use their
> > brains.
>
> I equate "unsafe" or "fragile" with "bad". There's no reason to use our
> brains for remembering what's safe or not when we can just remove unsafe
> things from the available APIs, and/or lean on the compiler to help
> (e.g. CONFIG_FORTIFY_SOURCE).
>
> Most of the uses of strcpy() in the kernel are just copying between two
> known-at-compile-time NUL-terminated character arrays. We had wanted to
> introduce stracpy() for this, but Linus objected to yet more string
> functions. So for now, I'm aimed at removing strlcpy() completely first,
> then look at strcpy() -> strscpy() for cases where target size is NOT
> compile-time known, and then to convert the kernel's strcpy() into
> _requiring_ that source/dest lengths are known at compile time.
>
> And then tackle strncpy(), which is a mess.

In general it's better to have a robust API, but what may go wrong
with the interface where we have no length of  the buffer passed, but
we all know that it's PAGE_SIZE?
So, what's wrong with doing something like
strcpy(buf, "Yes, we know we won't overflow here\n");
?


-- 
With Best Regards,
Andy Shevchenko