linux-kernel - Re: [PATCH v5 4/5] Add new file in LKDTM to test fortified strscpy.

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Date:   Thu, 19 Nov 2020 17:29:42 +0100
From:   Francis Laniel <laniel_francis@...vacyrequired.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     akpm@...ux-foundation.org, linux-hardening@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org, dja@...ens.net
Subject: Re: [PATCH v5 4/5] Add new file in LKDTM to test fortified strscpy.

Le mercredi 18 novembre 2020, 21:02:32 CET Kees Cook a écrit :
> On Wed, Nov 18, 2020 at 12:07:30PM +0100, laniel_francis@...vacyrequired.com 
wrote:
> > From: Francis Laniel <laniel_francis@...vacyrequired.com>
> > 
> > This new test ensures that fortified strscpy has the same behavior than
> > vanilla strscpy (e.g. returning -E2BIG when src content is truncated).
> > Finally, it generates a crash at runtime because there is a write overflow
> > in destination string.
> > 
> > Signed-off-by: Francis Laniel <laniel_francis@...vacyrequired.com>
> > Reviewed-by: Kees Cook <keescook@...omium.org>
> > ---
> > 
> >  drivers/misc/lkdtm/Makefile             |  1 +
> >  drivers/misc/lkdtm/core.c               |  1 +
> >  drivers/misc/lkdtm/fortify.c            | 82 +++++++++++++++++++++++++
> >  drivers/misc/lkdtm/lkdtm.h              |  3 +
> >  tools/testing/selftests/lkdtm/tests.txt |  1 +
> >  5 files changed, 88 insertions(+)
> >  create mode 100644 drivers/misc/lkdtm/fortify.c
> > 
> > diff --git a/drivers/misc/lkdtm/Makefile b/drivers/misc/lkdtm/Makefile
> > index c70b3822013f..d898f7b22045 100644
> > --- a/drivers/misc/lkdtm/Makefile
> > +++ b/drivers/misc/lkdtm/Makefile
> > @@ -10,6 +10,7 @@ lkdtm-$(CONFIG_LKDTM)		+= rodata_objcopy.o
> > 
> >  lkdtm-$(CONFIG_LKDTM)		+= usercopy.o
> >  lkdtm-$(CONFIG_LKDTM)		+= stackleak.o
> >  lkdtm-$(CONFIG_LKDTM)		+= cfi.o
> > 
> > +lkdtm-$(CONFIG_LKDTM)		+= fortify.o
> > 
> >  KASAN_SANITIZE_stackleak.o	:= n
> >  KCOV_INSTRUMENT_rodata.o	:= n
> > 
> > diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c
> > index b8c51a633fcc..3c0a67f072c0 100644
> > --- a/drivers/misc/lkdtm/core.c
> > +++ b/drivers/misc/lkdtm/core.c
> > @@ -175,6 +175,7 @@ static const struct crashtype crashtypes[] = {
> > 
> >  	CRASHTYPE(USERCOPY_KERNEL),
> >  	CRASHTYPE(STACKLEAK_ERASING),
> >  	CRASHTYPE(CFI_FORWARD_PROTO),
> > 
> > +	CRASHTYPE(FORTIFIED_STRSCPY),
> > 
> >  #ifdef CONFIG_X86_32
> >  
> >  	CRASHTYPE(DOUBLE_FAULT),
> >  
> >  #endif
> > 
> > diff --git a/drivers/misc/lkdtm/fortify.c b/drivers/misc/lkdtm/fortify.c
> > new file mode 100644
> > index 000000000000..790d46591bf5
> > --- /dev/null
> > +++ b/drivers/misc/lkdtm/fortify.c
> > @@ -0,0 +1,82 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (c) 2020 Francis Laniel <laniel_francis@...vacyrequired.com>
> > + *
> > + * Add tests related to fortified functions in this file.
> > + */
> > +#include <linux/string.h>
> > +#include <linux/slab.h>
> > +#include "lkdtm.h"
> 
> Ah, I just noticed one small nit here during build testing: lkdtm.h
> needs to be included first to get the correct pr_fmt to avoid a warning:
> 
> In file included from drivers/misc/lkdtm/fortify.c:9:
> drivers/misc/lkdtm/lkdtm.h:5: warning: "pr_fmt" redefined
>     5 | #define pr_fmt(fmt) "lkdtm: " fmt
> 
> -Kees

This my bad, I noticed this warning but though it was "normal" with LKDTM.
I should have asked about it!

I will send the v6 soon!