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    Subject[PATCH 4.18 07/34] cachefiles: fix the race between cachefiles_bury_object() and rmdir(2)
    Date
    4.18-stable review patch.  If anyone has any objections, please let me know.

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

    From: Al Viro <viro@zeniv.linux.org.uk>

    commit 169b803397499be85bdd1e3d07d6f5e3d4bd669e upstream.

    the victim might've been rmdir'ed just before the lock_rename();
    unlike the normal callers, we do not look the source up after the
    parents are locked - we know it beforehand and just recheck that it's
    still the child of what used to be its parent. Unfortunately,
    the check is too weak - we don't spot a dead directory since its
    ->d_parent is unchanged, dentry is positive, etc. So we sail all
    the way to ->rename(), with hosting filesystems _not_ expecting
    to be asked renaming an rmdir'ed subdirectory.

    The fix is easy, fortunately - the lock on parent is sufficient for
    making IS_DEADDIR() on child safe.

    Cc: stable@vger.kernel.org
    Fixes: 9ae326a69004 (CacheFiles: A cache that backs onto a mounted filesystem)
    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: David Howells <dhowells@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/cachefiles/namei.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/fs/cachefiles/namei.c
    +++ b/fs/cachefiles/namei.c
    @@ -343,7 +343,7 @@ try_again:
    trap = lock_rename(cache->graveyard, dir);

    /* do some checks before getting the grave dentry */
    - if (rep->d_parent != dir) {
    + if (rep->d_parent != dir || IS_DEADDIR(d_inode(rep))) {
    /* the entry was probably culled when we dropped the parent dir
    * lock */
    unlock_rename(cache->graveyard, dir);

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