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SubjectRe: [PATCH] loop: prevent bdev freeing while device in use
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Hi

On Mon, Apr 1, 2013 at 3:53 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Mon, Apr 1, 2013 at 10:00 AM, Anatol Pomozov
> <anatol.pomozov@gmail.com> wrote:
>> Hi
>>
>> On Mon, Apr 1, 2013 at 8:16 AM, Linus Torvalds
>> <torvalds@linux-foundation.org> wrote:
>>> On Mon, Apr 1, 2013 at 4:58 AM, Anatol Pomozov <anatol.pomozov@gmail.com> wrote:
>>>>
>>>> To prevent use-after-free we need to hold device inode in loop_set_fd()
>>>> and put it later in loop_clr_fd().
>>>
>>> Is there something that guarantees that there's only one loop_set_fd()
>>> and one paired loop_clr_fd()?
>>
>> Yes there is such guarantee.
>>
>> Every time we call loop_set_fd() we check that loop_device->lo_state
>> is Lo_unbound and set it to Lo_bound If somebody will try to set_fd
>> again it will get EBUSY. And if we try to loop_clr_fd() on unbound
>> loop device we'll get ENXIO.
>>
>> loop_set_fd/loop_clr_fd (and any other loop ioctl) is called under
>> loop_device->lo_ctl_mutex.
>
> Ok, good enough for me, I applied it, and it's commit
> c1681bf8a7b1b98edee8b862a42c19c4e53205fd in my tree.
>
> I assume it should go to stable too, because none of this is new, is
> it? Did you check how far back this applies? I assume this goes back
> pretty much forever, no?

I bisected kernel using test from my commit and it points to
4c823cc3d568277aa6340d8df6981e34f4c4dee5 (appeared in kernel 3.2).

But even despite i cannot repro the crash on 3.0-stable, the
underlying issue (block_device is not locked) still exists there. So I
think patch should go to stable as well.


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