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From: John Hubbard <jhubbard@nvidia.com>
To: Michal Hocko <mhocko@kernel.org>, Jann Horn <jannh@google.com>
Cc: Linux-MM <linux-mm@kvack.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Khalid Aziz <khalid.aziz@oracle.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Russell King - ARM Linux <linux@armlinux.org.uk>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Florian Weimer <fweimer@redhat.com>,
	Matthew Wilcox <willy@infradead.org>,
	<abdhalee@linux.vnet.ibm.com>, <joel@jms.id.au>,
	Kees Cook <keescook@chromium.org>, <jasone@google.com>,
	<davidtgoldblatt@gmail.com>, <trasz@freebsd.org>,
	Anshuman Khandual <khandual@linux.vnet.ibm.com>,
	Daniel Micay <danielmicay@gmail.com>,
	kernel list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: don't clobber partially overlapping VMA with MAP_FIXED_NOREPLACE
Date: Wed, 10 Oct 2018 11:03:49 -0700	[thread overview]
Message-ID: <93ee9489-d4cc-70e2-40fa-c78cf17add9a@nvidia.com> (raw)
In-Reply-To: <20181010173857.GM5873@dhcp22.suse.cz>

On 10/10/18 10:38 AM, Michal Hocko wrote:
> On Wed 10-10-18 19:26:50, Jann Horn wrote:
> [...]
>> As you can see, the first page of the mapping at 0x10001000 was clobbered.
>>
>>>> diff --git a/mm/mmap.c b/mm/mmap.c
>>>> index 5f2b2b184c60..f7cd9cb966c0 100644
>>>> --- a/mm/mmap.c
>>>> +++ b/mm/mmap.c
>>>> @@ -1410,7 +1410,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
>>>>       if (flags & MAP_FIXED_NOREPLACE) {
>>>>               struct vm_area_struct *vma = find_vma(mm, addr);
>>>>
>>>> -             if (vma && vma->vm_start <= addr)
>>>> +             if (vma && vma->vm_start < addr + len)
>>>
>>> find_vma is documented to - Look up the first VMA which satisfies addr <
>>> vm_end, NULL if none.
>>> This means that the above check guanratees that
>>>         vm_start <= addr < vm_end
>>> so an overlap is guanrateed. Why should we care how much we overlap?
>>
>> "an overlap is guaranteed"? I have no idea what you're trying to say.
> 
> I have misread your changelog and the patch. Sorry about that. I thought
> you meant a false possitive but you in fact meant false negative. Now it
> makes complete sense.
> 
> Acked-by: Michal Hocko <mhocko@suse.com>
> 
> And thanks a lot for catching that!
> 

This also looks good to me. 

thanks,
-- 
John Hubbard
NVIDIA

WARNING: multiple messages have this Message-ID (diff)
From: John Hubbard <jhubbard@nvidia.com>
To: Michal Hocko <mhocko@kernel.org>, Jann Horn <jannh@google.com>
Cc: Linux-MM <linux-mm@kvack.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Khalid Aziz <khalid.aziz@oracle.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Russell King - ARM Linux <linux@armlinux.org.uk>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Florian Weimer <fweimer@redhat.com>,
	Matthew Wilcox <willy@infradead.org>,
	abdhalee@linux.vnet.ibm.com, joel@jms.id.au,
	Kees Cook <keescook@chromium.org>,
	jasone@google.com, davidtgoldblatt@gmail.com, trasz@freebsd.org,
	Anshuman Khandual <khandual@linux.vnet.ibm.com>,
	Daniel Micay <danielmicay@gmail.com>,
	kernel list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: don't clobber partially overlapping VMA with MAP_FIXED_NOREPLACE
Date: Wed, 10 Oct 2018 11:03:49 -0700	[thread overview]
Message-ID: <93ee9489-d4cc-70e2-40fa-c78cf17add9a@nvidia.com> (raw)
In-Reply-To: <20181010173857.GM5873@dhcp22.suse.cz>

On 10/10/18 10:38 AM, Michal Hocko wrote:
> On Wed 10-10-18 19:26:50, Jann Horn wrote:
> [...]
>> As you can see, the first page of the mapping at 0x10001000 was clobbered.
>>
>>>> diff --git a/mm/mmap.c b/mm/mmap.c
>>>> index 5f2b2b184c60..f7cd9cb966c0 100644
>>>> --- a/mm/mmap.c
>>>> +++ b/mm/mmap.c
>>>> @@ -1410,7 +1410,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
>>>>       if (flags & MAP_FIXED_NOREPLACE) {
>>>>               struct vm_area_struct *vma = find_vma(mm, addr);
>>>>
>>>> -             if (vma && vma->vm_start <= addr)
>>>> +             if (vma && vma->vm_start < addr + len)
>>>
>>> find_vma is documented to - Look up the first VMA which satisfies addr <
>>> vm_end, NULL if none.
>>> This means that the above check guanratees that
>>>         vm_start <= addr < vm_end
>>> so an overlap is guanrateed. Why should we care how much we overlap?
>>
>> "an overlap is guaranteed"? I have no idea what you're trying to say.
> 
> I have misread your changelog and the patch. Sorry about that. I thought
> you meant a false possitive but you in fact meant false negative. Now it
> makes complete sense.
> 
> Acked-by: Michal Hocko <mhocko@suse.com>
> 
> And thanks a lot for catching that!
> 

This also looks good to me. 

thanks,
-- 
John Hubbard
NVIDIA

  reply	other threads:[~2018-10-10 18:03 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-10 15:27 [PATCH] mm: don't clobber partially overlapping VMA with MAP_FIXED_NOREPLACE Jann Horn
2018-10-10 17:19 ` Michal Hocko
2018-10-10 17:26   ` Jann Horn
2018-10-10 17:38     ` Michal Hocko
2018-10-10 18:03       ` John Hubbard [this message]
2018-10-10 18:03         ` John Hubbard
2018-10-10 18:17     ` John Hubbard
2018-10-10 18:17       ` John Hubbard
2018-10-12 10:23     ` Michael Ellerman
2018-10-12 12:09       ` Jann Horn
2018-10-10 18:36 ` Kees Cook
2018-10-12 12:03 ` Vlastimil Babka
2018-10-15  7:47 ` Khalid Aziz

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