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jbd/jbd2: validate sb->s_first in journal_get_superblock()

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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>
This commit is contained in:
Eryu Guan 2011-11-01 19:04:59 -04:00 committed by Theodore Ts'o
parent bf52c6f7af
commit 8762202dd0
2 changed files with 16 additions and 0 deletions
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8
fs/jbd/journal.c
View file

@ -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:

8
fs/jbd2/journal.c
View file

@ -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: