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From: Kees Cook <keescook@chromium.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Hector Marco-Gisbert <hecmargi@upv.es>,
	Ismael Ripoll Ripoll <iripoll@upv.es>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Chen Gang <gang.chen.5i5j@gmail.com>,
	Michal Hocko <mhocko@suse.com>,
	Konstantin Khlebnikov <koct9i@gmail.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] mm: refuse wrapped vm_brk requests
Date: Tue, 12 Jul 2016 13:15:14 -0400	[thread overview]
Message-ID: <CAGXu5j+oZ49K0omm-7yMsR_kFYD-DQcYG8f+urS+TumzFYXR_w@mail.gmail.com> (raw)
In-Reply-To: <20160712133942.GA28837@redhat.com>

On Tue, Jul 12, 2016 at 9:39 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> On 07/11, Kees Cook wrote:
>>
>> On Mon, Jul 11, 2016 at 8:28 AM, Oleg Nesterov <oleg@redhat.com> wrote:
>> >
>> > and thus this patch fixes the error code returned by do_brk() in case
>> > of overflow, now it returns -ENOMEM rather than zero. Perhaps
>> >
>> >         if (!len)
>> >                 return 0;
>> >         len = PAGE_ALIGN(len);
>> >         if (!len)
>> >                 return -ENOMEM;
>> >
>> > would be more clear but this is subjective.
>>
>> I'm fine either way.
>
> Me too, so feel free to ignore,
>
>> > I am wondering if we should shift this overflow check to the caller(s).
>> > Say, sys_brk() does find_vma_intersection(mm, oldbrk, newbrk+PAGE_SIZE)
>> > before do_brk(), and in case of overflow find_vma_intersection() can
>> > wrongly return NULL.
>> >
>> > Then do_brk() will be called with len = -oldbrk, this can overflow or
>> > not but in any case this doesn't look right too.
>> >
>> > Or I am totally confused?
>>
>> I think the callers shouldn't request a negative value, sure, but
>> vm_brk should notice and refuse it.
>
> Not sure I understand...
>
> I tried to say that, with or without this change, sys_brk() should check
> for overflow too, otherwise it looks buggy.

Hmm, it's not clear to me the right way to fix sys_brk(), but it looks
like my change to do_brk() would catch the problem?

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security

WARNING: multiple messages have this Message-ID (diff)
From: Kees Cook <keescook@chromium.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Hector Marco-Gisbert <hecmargi@upv.es>,
	Ismael Ripoll Ripoll <iripoll@upv.es>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Chen Gang <gang.chen.5i5j@gmail.com>,
	Michal Hocko <mhocko@suse.com>,
	Konstantin Khlebnikov <koct9i@gmail.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] mm: refuse wrapped vm_brk requests
Date: Tue, 12 Jul 2016 13:15:14 -0400	[thread overview]
Message-ID: <CAGXu5j+oZ49K0omm-7yMsR_kFYD-DQcYG8f+urS+TumzFYXR_w@mail.gmail.com> (raw)
In-Reply-To: <20160712133942.GA28837@redhat.com>

On Tue, Jul 12, 2016 at 9:39 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> On 07/11, Kees Cook wrote:
>>
>> On Mon, Jul 11, 2016 at 8:28 AM, Oleg Nesterov <oleg@redhat.com> wrote:
>> >
>> > and thus this patch fixes the error code returned by do_brk() in case
>> > of overflow, now it returns -ENOMEM rather than zero. Perhaps
>> >
>> >         if (!len)
>> >                 return 0;
>> >         len = PAGE_ALIGN(len);
>> >         if (!len)
>> >                 return -ENOMEM;
>> >
>> > would be more clear but this is subjective.
>>
>> I'm fine either way.
>
> Me too, so feel free to ignore,
>
>> > I am wondering if we should shift this overflow check to the caller(s).
>> > Say, sys_brk() does find_vma_intersection(mm, oldbrk, newbrk+PAGE_SIZE)
>> > before do_brk(), and in case of overflow find_vma_intersection() can
>> > wrongly return NULL.
>> >
>> > Then do_brk() will be called with len = -oldbrk, this can overflow or
>> > not but in any case this doesn't look right too.
>> >
>> > Or I am totally confused?
>>
>> I think the callers shouldn't request a negative value, sure, but
>> vm_brk should notice and refuse it.
>
> Not sure I understand...
>
> I tried to say that, with or without this change, sys_brk() should check
> for overflow too, otherwise it looks buggy.

Hmm, it's not clear to me the right way to fix sys_brk(), but it looks
like my change to do_brk() would catch the problem?

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security

--
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  reply	other threads:[~2016-07-12 17:15 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-07-08 21:48 [PATCH 0/2] binfmt_elf: fix calculations for bss padding Kees Cook
2016-07-08 21:48 ` Kees Cook
2016-07-08 21:48 ` [PATCH 1/2] " Kees Cook
2016-07-08 21:48   ` Kees Cook
2016-07-12 22:32   ` Kees Cook
2016-07-12 22:32     ` Kees Cook
2016-07-08 21:48 ` [PATCH 2/2] mm: refuse wrapped vm_brk requests Kees Cook
2016-07-08 21:48   ` Kees Cook
2016-07-11 12:28   ` Oleg Nesterov
2016-07-11 12:28     ` Oleg Nesterov
2016-07-11 18:01     ` Kees Cook
2016-07-11 18:01       ` Kees Cook
2016-07-12 13:39       ` Oleg Nesterov
2016-07-12 13:39         ` Oleg Nesterov
2016-07-12 17:15         ` Kees Cook [this message]
2016-07-12 17:15           ` Kees Cook
2016-07-13 17:00           ` Oleg Nesterov
2016-07-13 17:00             ` Oleg Nesterov

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