linux-ext4 - Re: [PATCH] jbd2: clear BH_Delay & BH_Unwritten in journal_unmap

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Date:	Tue, 07 Feb 2012 22:34:59 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] jbd2: clear BH_Delay & BH_Unwritten in journal_unmap_buffer

On 2/7/12 4:07 PM, Eric Sandeen wrote:
> journal_unmap_buffer()'s zap_buffer: code clears a lot of buffer head
> state ala discard_buffer(), but does not touch _Delay or _Unwritten
> as discard_buffer() does.
> 
> This can be problematic in some areas of the ext4 code which assume
> that if they have found a buffer marked unwritten or delay, then it's
> a live one.  Perhaps those spots should check whether it is mapped
> as well, but if jbd2 is going to tear down a buffer, let's really
> tear it down completely.
> 
> Without this I get some fsx failures on sub-page-block filesystems
> up until v3.2, at which point 4e96b2dbbf1d7e81f22047a50f862555a6cb87cb
> and 189e868fa8fdca702eb9db9d8afc46b5cb9144c9 make the failures go
> away, because buried within that large change is some more flag
> clearing.  I still think it's worth doing in jbd2, since
> ->invalidatepage leads here directly, and it's the right place
> to clear away these flags.

Addresses CVE-2011-4086 BTW.

> Signed-off-by: Eric Sandeen <sandeen@...hat.com>
> Cc: stable@...r.kernel.org
> ---
> 
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index 35ae096..52653306 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -1949,6 +1949,8 @@ zap_buffer_unlocked:
>  	clear_buffer_mapped(bh);
>  	clear_buffer_req(bh);
>  	clear_buffer_new(bh);
> +	clear_buffer_delay(bh);
> +	clear_buffer_unwritten(bh);
>  	bh->b_bdev = NULL;
>  	return may_free;
>  }
> 
> 
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