linux-hardening - Re: [PATCH] drivers/input: Remove all strcpy() uses in favor of strscpy()

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Date:   Sat, 7 Aug 2021 16:02:45 +0200
From:   Len Baker <len.baker@....com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Len Baker <len.baker@....com>,
        "Russell King (Oracle)" <linux@...linux.org.uk>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, linux-hardening@...r.kernel.org,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        Joe Perches <joe@...ches.com>
Subject: Re: [PATCH] drivers/input: Remove all strcpy() uses in favor of
 strscpy()

Hi,

On Sun, Aug 01, 2021 at 09:44:33AM -0700, Kees Cook wrote:
> On Sun, Aug 01, 2021 at 05:57:32PM +0200, Len Baker wrote:
> > Hi,
> >
> > On Sun, Aug 01, 2021 at 04:00:00PM +0100, Russell King (Oracle) wrote:
> > > Rather than converting every single strcpy() in the kernel to
> > > strscpy(), maybe there should be some consideration given to how the
> > > issue of a strcpy() that overflows the buffer should be handled.
> > > E.g. in the case of a known string such as the above, if it's longer
> > > than the destination, should we find a way to make the compiler issue
> > > a warning at compile time?
> >
> > Good point. I am a kernel newbie and have no experience. So this
> > question should be answered by some kernel hacker :) But I agree
> > with your proposals.
> >
> > Kees and folks: Any comments?
> >
> > Note: Kees is asked the same question in [2]
> >
> > [2] https://lore.kernel.org/lkml/20210731135957.GB1979@titan/
>
> Hi!
>
> Sorry for the delay at looking into this. It didn't use to be a problem
> (there would always have been a compile-time warning generated for
> known-too-small cases), but that appears to have regressed when,
> ironically, strscpy() coverage was added. I've detailed it in the bug
> report:
> https://github.com/KSPP/linux/issues/88
>
> So, bottom line: we need to fix the missing compile-time warnings for
> strcpy() and strscpy() under CONFIG_FORTIFY_SOURCE=y.
>
> In the past we'd tried to add a stracpy()[1] that would only work with
> const string sources. Linus got angry[2] about API explosion, though,
> so we're mostly faced with doing the strscpy() replacements.
>
> Another idea might be to have strcpy() do the "constant strings only"
> thing, leaving strscpy() for the dynamic lengths.
>
> One thing is clear: replacing strlcpy() with strscpy() is probably the
> easiest and best first step to cleaning up the proliferation of str*()
> functions.

Thanks for all this info. I will work on it (clean up the proliferation
of str*() functions).

Regards,
Len

>
> -Kees
>
> [1] https://lore.kernel.org/lkml/ed4611a4a96057bf8076856560bfbf9b5e95d390.1563889130.git.joe@perches.com/
> [2] https://lore.kernel.org/lkml/CAHk-=wgqQKoAnhmhGE-2PBFt7oQs9LLAATKbYa573UO=DPBE0Q@mail.gmail.com/
>
> --
> Kees Cook