linux-kernel - Re: [PATCH] loop: prevent bdev freeing while device in use

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Date:	Mon, 1 Apr 2013 15:53:25 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Anatol Pomozov <anatol.pomozov@...il.com>,
	stable <stable@...r.kernel.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Theodore Ts'o" <tytso@....edu>, Salman Qazi <sqazi@...gle.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Guo Chao <yan@...ux.vnet.ibm.com>
Subject: Re: [PATCH] loop: prevent bdev freeing while device in use

On Mon, Apr 1, 2013 at 10:00 AM, Anatol Pomozov
<anatol.pomozov@...il.com> wrote:
> Hi
>
> On Mon, Apr 1, 2013 at 8:16 AM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
>> On Mon, Apr 1, 2013 at 4:58 AM, Anatol Pomozov <anatol.pomozov@...il.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?

               Linus
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