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    Subject[PATCH 4.14 261/267] ext4: work around deleting a file with i_nlink == 0 safely
    Date
    From: Theodore Ts'o <tytso@mit.edu>

    commit c7df4a1ecb8579838ec8c56b2bb6a6716e974f37 upstream.

    If the file system is corrupted such that a file's i_links_count is
    too small, then it's possible that when unlinking that file, i_nlink
    will already be zero. Previously we were working around this kind of
    corruption by forcing i_nlink to one; but we were doing this before
    trying to delete the directory entry --- and if the file system is
    corrupted enough that ext4_delete_entry() fails, then we exit with
    i_nlink elevated, and this causes the orphan inode list handling to be
    FUBAR'ed, such that when we unmount the file system, the orphan inode
    list can get corrupted.

    A better way to fix this is to simply skip trying to call drop_nlink()
    if i_nlink is already zero, thus moving the check to the place where
    it makes the most sense.

    https://bugzilla.kernel.org/show_bug.cgi?id=205433

    Link: https://lore.kernel.org/r/20191112032903.8828-1-tytso@mit.edu
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Cc: stable@kernel.org
    Reviewed-by: Andreas Dilger <adilger@dilger.ca>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/ext4/namei.c | 11 +++++------
    1 file changed, 5 insertions(+), 6 deletions(-)

    --- a/fs/ext4/namei.c
    +++ b/fs/ext4/namei.c
    @@ -3065,18 +3065,17 @@ static int ext4_unlink(struct inode *dir
    if (IS_DIRSYNC(dir))
    ext4_handle_sync(handle);

    - if (inode->i_nlink == 0) {
    - ext4_warning_inode(inode, "Deleting file '%.*s' with no links",
    - dentry->d_name.len, dentry->d_name.name);
    - set_nlink(inode, 1);
    - }
    retval = ext4_delete_entry(handle, dir, de, bh);
    if (retval)
    goto end_unlink;
    dir->i_ctime = dir->i_mtime = current_time(dir);
    ext4_update_dx_flag(dir);
    ext4_mark_inode_dirty(handle, dir);
    - drop_nlink(inode);
    + if (inode->i_nlink == 0)
    + ext4_warning_inode(inode, "Deleting file '%.*s' with no links",
    + dentry->d_name.len, dentry->d_name.name);
    + else
    + drop_nlink(inode);
    if (!inode->i_nlink)
    ext4_orphan_add(handle, inode);
    inode->i_ctime = current_time(inode);

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