Re: [PATCH 1/2] jbd/jbd2: validate sb->s_first in journal_get_superblock()

[Jan Kara <jack@suse.cz>]

On Tue 01-11-11 10:05:03, Eryu Guan wrote:
> I hit a J_ASSERT(blocknr != 0) failure in cleanup_journal_tail() when
> mounting a fsfuzzed ext3 image. It turns out that the corrupted ext3
> image has s_first = 0 in journal superblock, and the 0 is passed to
> journal->j_head in journal_reset(), then to blocknr in
> cleanup_journal_tail(), in the end the J_ASSERT failed.
> 
> So validate s_first after reading journal superblock from disk in
> journal_get_superblock() to ensure s_first is valid.
> 
> The following script could reproduce it:
> 
> fstype=ext3
> blocksize=1024
> img=$fstype.img
> offset=0
> found=0
> magic="c0 3b 39 98"
> 
> dd if=/dev/zero of=$img bs=1M count=8
> mkfs -t $fstype -b $blocksize -F $img
> filesize=`stat -c %s $img`
> while [ $offset -lt $filesize ]
> do
>         if od -j $offset -N 4 -t x1 $img | grep -i "$magic";then
>                 echo "Found journal: $offset"
>                 found=1
>                 break
>         fi
>         offset=`echo "$offset+$blocksize" | bc`
> done
> 
> if [ $found -ne 1 ];then
>         echo "Magic \"$magic\" not found"
>         exit 1
> fi
> 
> dd if=/dev/zero of=$img seek=$(($offset+23)) conv=notrunc bs=1 count=1
> 
> mkdir -p ./mnt
> mount -o loop $img ./mnt
  Thanks. I've fixed-up the style problems pointed out by Andreas and added
the patch to my tree.

								Honza

> 
> Cc: Jan Kara <jack@suse.cz>
> Cc: "Theodore Ts'o" <tytso@mit.edu>
> Signed-off-by: Eryu Guan <guaneryu@gmail.com>
> ---
>  fs/jbd/journal.c  |    8 ++++++++
>  fs/jbd2/journal.c |    8 ++++++++
>  2 files changed, 16 insertions(+), 0 deletions(-)
> 
> diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
> index 9fe061f..0c401de 100644
> --- a/fs/jbd/journal.c
> +++ b/fs/jbd/journal.c
> @@ -1135,6 +1135,14 @@ static int journal_get_superblock(journal_t *journal)
>  		goto out;
>  	}
>  
> +	if (be32_to_cpu(sb->s_first) == 0 ||
> +		be32_to_cpu(sb->s_first) >= journal->j_maxlen) {
> +		printk(KERN_WARNING
> +			"JBD: Invalid start block of journal: %u\n",
> +			be32_to_cpu(sb->s_first));
> +		goto out;
> +	}
> +
>  	return 0;
>  
>  out:
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index f24df13..e2d0e13 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -1251,6 +1251,14 @@ static int journal_get_superblock(journal_t *journal)
>  		goto out;
>  	}
>  
> +	if (be32_to_cpu(sb->s_first) == 0 ||
> +		be32_to_cpu(sb->s_first) >= journal->j_maxlen) {
> +		printk(KERN_WARNING
> +			"JBD2: Invalid start block of journal: %u\n",
> +			be32_to_cpu(sb->s_first));
> +		goto out;
> +	}
> +
>  	return 0;
>  
>  out:
> -- 
> 1.7.7.1
> 
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR