linux-kernel - RE: [patch] lib: check for strcpy() overflows to fixed length buffers

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Date:	Mon, 5 May 2014 00:19:42 +0000
From:	"Zheng, Lv" <lv.zheng@...el.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"devel@...ica.org" <devel@...ica.org>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Kees Cook <keescook@...omium.org>,
	Dave Jones <davej@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Moore, Robert" <robert.moore@...el.com>,
	"RobertBMoore@...puserve.com" <RobertBMoore@...puserve.com>,
	"Box, David E" <david.e.box@...el.com>
Subject: RE: [patch] lib: check for strcpy() overflows to fixed length
 buffers

Hi,

> From: Dan Carpenter [mailto:dan.carpenter@...cle.com]
> Sent: Thursday, May 01, 2014 4:15 AM
> 
> On Wed, Apr 30, 2014 at 09:49:23PM +0200, Rafael J. Wysocki wrote:
> > On Wednesday, April 30, 2014 06:08:44 PM Dan Carpenter wrote:
> > > There are sometimes where we know that we are doing an strcpy() into a
> > > fixed length buffer.  In those cases, we could verify that the strcpy()
> > > doesn't overflow.  This patch introduces DEBUG_STRICT_SLOW_STRCPY_CHECKS
> > > if you want to check for that.  The downside is that it makes strcpy
> > > slower.
> > >
> > > I introduced __compiletime_size() to make this work.  It returns the
> > > size of the destination buffer or zero if the size isn't known.  The
> > > __compiletime_object_size() is similar but if you pass it a struct
> > > member then it returns the size of everything from there to the end of
> > > the struct.  Another difference is __compiletime_object_size() returns
> > > -1 for unknown sizes.
> > >
> > > If you pass a char pointer to __compiletime_size() then it returns zero.
> > >
> > > The strcpy() check ignores buffers with just one byte because people
> > > often use those for variable length strings at the end of a struct.
> > >
> > > I have tested this patch lightly and created some bugs for it to detect
> > > but I have not detected any real life overflows.
> > >
> > > Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> > >
> > > diff --git a/include/acpi/platform/acenv.h b/include/acpi/platform/acenv.h
> > > index e863dd5..5e0fc2b 100644
> > > --- a/include/acpi/platform/acenv.h
> > > +++ b/include/acpi/platform/acenv.h
> >
> > This is an ACPICA header and changes to it need to be submitted to the ACPICA
> > maintainers (as per MAINTAINERS).  We only get ACPICA changes from the
> > upstream project (except for really special situations).
> 
> Ok.  I should have added Robert and Lv to the CC list.  My guess is
> that the (void) is needed to avoid compile warnings but it's needed for
> us to avoid compile breakage with this change.

In normal ACPICA build environment, I didn't suffer from new build errors after deleting this "void".
But this might be required by lint users.
You can split ACPICA changes into a separate patch so that it could be easily reverted if someone complained.

Thanks
-Lv

> 
> Anyway, I'll wait for a couple days and resend that bit broken out.
> 
> regards,
> dan carpenter
> 
> >
> > > @@ -320,7 +320,7 @@
> > >  #define ACPI_STRSTR(s1,s2)      strstr((s1), (s2))
> > >  #define ACPI_STRCHR(s1,c)       strchr((s1), (c))
> > >  #define ACPI_STRLEN(s)          (acpi_size) strlen((s))
> > > -#define ACPI_STRCPY(d,s)        (void) strcpy((d), (s))
> > > +#define ACPI_STRCPY(d,s)        strcpy((d), (s))
> > >  #define ACPI_STRNCPY(d,s,n)     (void) strncpy((d), (s), (acpi_size)(n))
> > >  #define ACPI_STRNCMP(d,s,n)     strncmp((d), (s), (acpi_size)(n))
> > >  #define ACPI_STRCMP(d,s)        strcmp((d), (s))
> >
> > Thanks!
> >
> > --
> > I speak only for myself.
> > Rafael J. Wysocki, Intel Open Source Technology Center.
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