jbd/jbd2: validate sb->s_first in journal_get_superblock()
authorEryu Guan <guaneryu@gmail.com>
Tue, 1 Nov 2011 23:04:59 +0000 (19:04 -0400)
committerTheodore Ts'o <tytso@mit.edu>
Tue, 1 Nov 2011 23:04:59 +0000 (19:04 -0400)
commit8762202dd0d6e46854f786bdb6fb3780a1625efe
tree0fe3a7e102bfefa0bbb5810f934fbf93840459dd
parentbf52c6f7af55c48ab0fd5f990460b884b428d906
jbd/jbd2: validate sb->s_first in journal_get_superblock()

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>
fs/jbd/journal.c
fs/jbd2/journal.c