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>
2 files changed