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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAOMFOmUDuBomyp-kVRc3m9FuJSwkpg25MNYKo5ckbWuOExsn=g@mail.gmail.com>
Date:	Mon, 1 Apr 2013 22:58:55 -0700
From:	Anatol Pomozov <anatol.pomozov@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ayan George <ayan@...n.net>
Cc:	stable <stable@...r.kernel.org>,
	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

Hi

On Mon, Apr 1, 2013 at 3:53 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> 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?

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.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/