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    Subject[PATCH 3.16 018/410] ext4: fail ext4_iget for root directory if unallocated
    3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Theodore Ts'o <tytso@mit.edu>

    commit 8e4b5eae5decd9dfe5a4ee369c22028f90ab4c44 upstream.

    If the root directory has an i_links_count of zero, then when the file
    system is mounted, then when ext4_fill_super() notices the problem and
    tries to call iput() the root directory in the error return path,
    ext4_evict_inode() will try to free the inode on disk, before all of
    the file system structures are set up, and this will result in an OOPS
    caused by a NULL pointer dereference.

    This issue has been assigned CVE-2018-1092.

    https://bugzilla.kernel.org/show_bug.cgi?id=199179
    https://bugzilla.redhat.com/show_bug.cgi?id=1560777

    Reported-by: Wen Xu <wen.xu@gatech.edu>
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    [bwh: Backported to 3.16: use EIO instead of EFSCORRUPTED]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    fs/ext4/inode.c | 6 ++++++
    1 file changed, 6 insertions(+)

    --- a/fs/ext4/inode.c
    +++ b/fs/ext4/inode.c
    @@ -4198,6 +4198,12 @@ struct inode *ext4_iget(struct super_blo
    goto bad_inode;
    raw_inode = ext4_raw_inode(&iloc);

    + if ((ino == EXT4_ROOT_INO) && (raw_inode->i_links_count == 0)) {
    + EXT4_ERROR_INODE(inode, "root inode unallocated");
    + ret = -EIO;
    + goto bad_inode;
    + }
    +
    if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
    ei->i_extra_isize = le16_to_cpu(raw_inode->i_extra_isize);
    if (EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize >
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