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    Subject[27/45] jbd/jbd2: validate sb->s_first in journal_get_superblock()
    3.0-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Eryu Guan <guaneryu@gmail.com>

    commit 8762202dd0d6e46854f786bdb6fb3780a1625efe upstream.

    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

    Cc: Jan Kara <jack@suse.cz>
    Signed-off-by: Eryu Guan <guaneryu@gmail.com>
    Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
    Cc: Moritz Mühlenhoff <jmm@inutil.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    fs/jbd/journal.c | 8 ++++++++
    fs/jbd2/journal.c | 8 ++++++++
    2 files changed, 16 insertions(+)

    --- a/fs/jbd/journal.c
    +++ b/fs/jbd/journal.c
    @@ -1131,6 +1131,14 @@ static int journal_get_superblock(journa
    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:
    --- a/fs/jbd2/journal.c
    +++ b/fs/jbd2/journal.c
    @@ -1251,6 +1251,14 @@ static int journal_get_superblock(journa
    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:

    --
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