linux-ext4 - Re: attempt to fix race in bigalloc code path

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: <CAGr1F2EG32dkeo+6DU4caQdJtFBLN7kpF9a4Gj_vr+awdGZ6jw@mail.gmail.com>
Date:	Mon, 22 Aug 2011 10:30:02 -0700
From:	Aditya Kali <adityakali@...gle.com>
To:	Yongqiang Yang <xiaoqiangnk@...il.com>
Cc:	Jan Kara <jack@...e.cz>, "Ted Ts'o" <tytso@....edu>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: attempt to fix race in bigalloc code path

On Mon, Aug 22, 2011 at 6:54 AM, Yongqiang Yang <xiaoqiangnk@...il.com> wrote:
> Hi,
>
> I can not find the patch - attempt to fix race in bigalloc code path -
> in the mailing list.
>
> I don't think this patch can work.  set_buffers_da_mapped() is called
> under i_data_sem, so it can not lock page.  If the page is not locked,
> calling page_has_buffers() is not secure as Jan pointed out
> previously.  If a page is partially mapped(block size < page size),
> setting BH_Da_Mapped without locking page is not safe too.
>
The BH_Da_Mapped is set only during page writeback when the page is
locked (in write_cache_pages_da). So, the setting of BH_Da_Mapped
should be safe, no ?

> BTW:  find_delalloc_range() does not lock page as ext4_fiemap_cb().
> As Jan said, it can crash system.  BUT we can not lock page in both
> scenarios, because i_data_sem is hold. So delayed extent list is
> necessary.  I have finished the code implementing delayed extent list,
> which needs some further testing.
>
>
> What are your opinions?
>
I agree that having a delayed extent list will greatly simply this
solution in this case.

>
> --
> Best Wishes
> Yongqiang Yang
>
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html