linux-kernel - Re: [PATCH 07/12] driver/char: use correct format characters

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Message-ID: <CAGG=3QV1DqiufpBRmUcYMEuH55OizMGLCcCiLhxaZ8FEwbn7gA@mail.gmail.com>
Date:   Mon, 13 Jun 2022 11:40:08 -0700
From:   Bill Wendling <morbo@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Bill Wendling <isanbard@...il.com>,
        Tony Luck <tony.luck@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Phillip Potter <phil@...lpotter.co.uk>,
        Arnd Bergmann <arnd@...db.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Jan Kara <jack@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        Ross Philipson <ross.philipson@...cle.com>,
        linux-edac@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        linux-mm@...ck.org, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, Networking <netdev@...r.kernel.org>,
        alsa-devel@...a-project.org,
        clang-built-linux <llvm@...ts.linux.dev>
Subject: Re: [PATCH 07/12] driver/char: use correct format characters

On Thu, Jun 9, 2022 at 10:18 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Thu, Jun 09, 2022 at 10:16:26PM +0000, Bill Wendling wrote:
> > From: Bill Wendling <isanbard@...il.com>
>
> Why isn't that matching your From: line in the email?
>
There must be something wrong with my .gitconfig file. I"ll check into it.

> >
> > When compiling with -Wformat, clang emits the following warnings:
>
> Is that ever a default build option for the kernel?
>
We want to enable -Wformat for clang. I believe that these specific
warnings have been disabled, but I'm confused as to why, because
they're valid warnings. When I compiled with the warning enabled,
there were only a few (12) places that needed changes, so thought that
patches would be a nice cleanup, even though the warning itself is
disabled.

> > drivers/char/mem.c:775:16: error: format string is not a string literal (potentially insecure) [-Werror,-Wformat-security]
> >                               NULL, devlist[minor].name);
> >                                     ^~~~~~~~~~~~~~~~~~~
> >
> > Use a string literal for the format string.
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/378
> > Signed-off-by: Bill Wendling <isanbard@...il.com>
> > ---
> >  drivers/char/mem.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/char/mem.c b/drivers/char/mem.c
> > index 84ca98ed1dad..32d821ba9e4d 100644
> > --- a/drivers/char/mem.c
> > +++ b/drivers/char/mem.c
> > @@ -772,7 +772,7 @@ static int __init chr_dev_init(void)
> >                       continue;
> >
> >               device_create(mem_class, NULL, MKDEV(MEM_MAJOR, minor),
> > -                           NULL, devlist[minor].name);
> > +                           NULL, "%s", devlist[minor].name);
>
> Please explain how this static string can ever be user controlled.
>
All someone would need to do is accidentally insert an errant '%' in
one of the strings for this function call to perform unexpected
actions---at the very least reading memory that's not allocated and
may contain garbage, thereby decreasing performance and possibly
overrunning some buffer. Perhaps in this specific scenario it's
unlikely, but "device_create()" is used in a lot more places than
here. This patch is a general code cleanup.

-bw