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
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.
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
<[email protected]> 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
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
> <[email protected]> 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
>
>
>
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 <[email protected]> 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
>> <[email protected]> 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
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 <[email protected]> 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
>>> <[email protected]> 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
Hi Dave,
I've updated the patch accordingly.
Regards,
Shankara
On Mon, Jun 4, 2018 at 11:39 AM, Dave Kleikamp <[email protected]> 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 <[email protected]> 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
>>>> <[email protected]> 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
Sorry,
Sent the same thing twice. Here is the updated one.
On Mon, Jun 4, 2018 at 1:22 PM, shankarapailoor
<[email protected]> wrote:
> Hi Dave,
>
> I've updated the patch accordingly.
>
> Regards,
> Shankara
>
> On Mon, Jun 4, 2018 at 11:39 AM, Dave Kleikamp <[email protected]> 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 <[email protected]> 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
>>>>> <[email protected]> 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