From: "H. Peter Anvin" <hpa@zytor.com>
To: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Stephen Boyd <sboyd@codeaurora.org>,
Arnd Bergmann <arnd@arndb.de>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
linux-parisc@vger.kernel.org, linux-s390@vger.kernel.org,
Arjan van de Ven <arjan@linux.intel.com>,
Helge Deller <deller@gmx.de>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
Chris Metcalf <cmetcalf@tilera.com>
Subject: Re: [PATCH] Consolidate CONFIG_DEBUG_STRICT_USER_COPY_CHECK
Date: Wed, 27 Feb 2013 14:52:57 -0800 [thread overview]
Message-ID: <512E8E49.3050206@zytor.com> (raw)
In-Reply-To: <20130228094510.3341017130e4476e046bdd22@canb.auug.org.au>
On 02/27/2013 02:45 PM, Stephen Rothwell wrote:
> Hi all,
>
> On Wed, 27 Feb 2013 14:19:16 -0800 "H. Peter Anvin" <hpa@zytor.com>
> wrote:
>>
>> Although some of the cases I have seen being flagged as "false
>> positives" have been real bugs.
>
> [hijacking the thread :-)]
>
> I have been getting this warning for a very long time ( which would
> be an error if CONFIG_DEBUG_STRICT_USER_COPY_CHECK was set):
>
> i386 defconfig i386-linux-gcc (GCC) 4.6.3
>
> In file included from arch/x86/include/asm/uaccess.h:537:0, from
> include/linux/uaccess.h:5, from include/linux/highmem.h:8, from
> include/linux/pagemap.h:10, from fs/binfmt_misc.c:27:
> arch/x86/include/asm/uaccess_32.h: In function
> 'parse_command.part.2': arch/x86/include/asm/uaccess_32.h:211:26:
> warning: call to 'copy_from_user_overflow' declared with attribute
> warning: copy_from_user() buffer size is not provably correct
> [enabled by default]
>
OK, that is surprising, because that copy is very clearly properly
guarded:
static int parse_command(const char __user *buffer, size_t count)
{
char s[4];
if (!count)
return 0;
if (count > 3)
return -EINVAL;
if (copy_from_user(s, buffer, count))
return -EFAULT;
It isn't possible for count to be anything other than 1, 2 or 3 there,
and it is very surprising that gcc can't see it.
This might be worth filing a gcc bug for.
-hpa
next prev parent reply other threads:[~2013-02-27 22:53 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-27 3:00 [PATCH] Consolidate CONFIG_DEBUG_STRICT_USER_COPY_CHECKS Stephen Boyd
2013-02-27 20:32 ` [PATCH] Consolidate CONFIG_DEBUG_STRICT_USER_COPY_CHECK Arnd Bergmann
2013-02-27 20:42 ` Stephen Boyd
2013-02-27 21:33 ` Arnd Bergmann
2013-02-27 22:19 ` H. Peter Anvin
2013-02-27 22:45 ` Stephen Rothwell
2013-02-27 22:52 ` H. Peter Anvin [this message]
2013-02-27 22:56 ` Arjan van de Ven
2013-02-27 22:52 ` Stephen Boyd
2013-02-27 22:55 ` H. Peter Anvin
2013-02-27 23:19 ` Stephen Boyd
2013-02-27 23:21 ` H. Peter Anvin
2013-02-27 22:41 ` [PATCH] Consolidate CONFIG_DEBUG_STRICT_USER_COPY_CHECKS Helge Deller
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