linux-kernel - Re: Slab out of bounds in setxattr

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Message-ID: <CAB+yDaar=-KTfO2i_aKY9R2xMXUpw=DNwr4sxGCC5nvP7w9YZQ@mail.gmail.com>
Date:   Mon, 4 Jun 2018 13:25:06 -0700
From:   shankarapailoor <shankarapailoor@...il.com>
To:     Dave Kleikamp <dave.kleikamp@...cle.com>
Cc:     jfs-discussion@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: Slab out of bounds in setxattr

Sorry,

Sent the same thing twice. Here is the updated one.

On Mon, Jun 4, 2018 at 1:22 PM, shankarapailoor
<shankarapailoor@...il.com> wrote:
> Hi Dave,
>
> I've updated the patch accordingly.
>
> Regards,
> Shankara
>
> On Mon, Jun 4, 2018 at 11:39 AM, Dave Kleikamp <dave.kleikamp@...cle.com> wrote:
>> On 06/04/2018 01:30 PM, shankarapailoor wrote:
>>> Hi Dave,
>>>
>>> Attached is my proposed patch. It solves the problem as you suggest
>>> and I don't see the KASAN complaint.
>>
>> That looks good to me. Add a description and a Signed-off-by: and I'll
>> get it pushed upstream.
>>
>> Thanks for finding this.
>>
>> Shaggy
>>
>>>
>>> Regards,
>>> Shankara
>>>
>>> On Mon, Jun 4, 2018 at 11:24 AM, Dave Kleikamp <dave.kleikamp@...cle.com> wrote:
>>>> On 06/01/2018 11:06 PM, shankarapailoor wrote:
>>>>> Hi,
>>>>>
>>>>> Looking at the crash some more, it seems that if value_len > PAGE_SIZE
>>>>> then e_buf->max_size is rounded up nearest page size [1]. If a new
>>>>> attribute is added with value_len < e_buf->max_size - EA_SIZE(ea) then
>>>>> no new space is allocated for the attiribute list [2] and this
>>>>> triggers the KASAN slab out of bounds error. This is the case in the C
>>>>> repro I provided.
>>>>
>>>> I see the problem. It looks like we should be calculating max_size
>>>> earlier and using that to call kmalloc(). (xattr.c#496)
>>>>
>>>> Shaggy
>>>>>
>>>>>
>>>>> 1. https://elixir.bootlin.com/linux/v4.17-rc7/source/fs/jfs/xattr.c#L501
>>>>> 2. https://elixir.bootlin.com/linux/v4.17-rc7/source/fs/jfs/xattr.c#L723
>>>>>
>>>>> On Fri, Jun 1, 2018 at 1:52 PM, shankarapailoor
>>>>> <shankarapailoor@...il.com> wrote:
>>>>>> Hi Dave et al,
>>>>>>
>>>>>> I have been fuzzing linux 4.17-rc4 with JFS using Syzkaller  KASAN:
>>>>>> slab-out-of-bounds in jfs_xattr.
>>>>>>
>>>>>> Attached are my kernel configs and a C reproducer. In the first
>>>>>> setxattr call it appears that length is much larger than the name. In
>>>>>> __jfs_setxattr, I don't see where the length is checked against the
>>>>>> actual value length.
>>>>>>
>>>>>> Regards,
>>>>>> Shankara Pailoor
>
>
>
> --
> Regards,
> Shankara Pailoor



-- 
Regards,
Shankara Pailoor

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