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Old 11-22-2011, 01:21 PM
Stefan Bader
 
Default ACK: jbd/jbd2: validate sb->s_first in journal_get_superblock()

On 22.11.2011 14:50, Andy Whitcroft wrote:
> From: Eryu Guan <guaneryu@gmail.com>
>
> 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>
>
> (cherry picked from commit 8762202dd0d6e46854f786bdb6fb3780a1625efe)
> CVE-2011-4132
> BugLink: http://bugs.launchpad.net/bugs/893148
> Signed-off-by: Andy Whitcroft <apw@canonical.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 5d14243..6ad18ba 100644
> --- a/fs/jbd/journal.c
> +++ b/fs/jbd/journal.c
> @@ -1030,6 +1030,14 @@ 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
",
> + be32_to_cpu(sb->s_first));
> + goto out;
> + }
> +
> return 0;
>
> out:
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 6ddc553..33eb17c 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -1029,6 +1029,14 @@ 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
",
> + be32_to_cpu(sb->s_first));
> + goto out;
> + }
> +
> return 0;
>
> out:

Looks ok

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