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

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Date:   Mon, 4 Jun 2018 11:30:36 -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

Hi Dave,

Attached is my proposed patch. It solves the problem as you suggest
and I don't see the KASAN complaint.

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

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