linux-ext4 - Re: [PATCH] ext4: Fix possible use after free of buffer head

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Message-ID: <20121129190239.GA2888@blackbox.djwong.org>
Date:	Thu, 29 Nov 2012 11:02:39 -0800
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	linux-ext4@...r.kernel.org, tytso@....edu, stable@...r.kernel.org
Subject: Re: [PATCH] ext4: Fix possible use after free of buffer head

On Thu, Nov 29, 2012 at 11:43:48AM +0100, Lukas Czerner wrote:
> Commit fa77dcfafeaa6bc73293c646bfc3d5192dcf0be2 introduces block bitmap
> checksum calculation into ext4_new_inode() in the case that block group
> was uninitialized. However we brelse() the bitmap buffer before we
> attempt to checksum it so we have no guarantee that the buffer is still
> there.
> 
> Fix this by releasing the buffer after the possible checksum
> computation.

Looks ok, so:
Acked-by: Darrick J. Wong <darrick.wong@...cle.com>

That IBM fellow is gone. ;)

--D
> 
> Signed-off-by: Lukas Czerner <lczerner@...hat.com>
> Cc: Darrick J. Wong <djwong@...ibm.com>
> Cc: stable@...r.kernel.org
> ---
>  fs/ext4/ialloc.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
> index 3a100e7..c7efa88 100644
> --- a/fs/ext4/ialloc.c
> +++ b/fs/ext4/ialloc.c
> @@ -762,7 +762,6 @@ got:
>  
>  		BUFFER_TRACE(block_bitmap_bh, "dirty block bitmap");
>  		err = ext4_handle_dirty_metadata(handle, NULL, block_bitmap_bh);
> -		brelse(block_bitmap_bh);
>  
>  		/* recheck and clear flag under lock if we still need to */
>  		ext4_lock_group(sb, group);
> @@ -775,6 +774,7 @@ got:
>  			ext4_group_desc_csum_set(sb, group, gdp);
>  		}
>  		ext4_unlock_group(sb, group);
> +		brelse(block_bitmap_bh);
>  
>  		if (err)
>  			goto fail;
> -- 
> 1.7.7.6
> 
> --
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