• Maxim Patlasov's avatar
    fs/pnode.c: treat zero mnt_group_id-s as unequal · f4e8208d
    Maxim Patlasov authored
    commit 7ae8fd03 upstream.
    
    propagate_one(m) calculates "type" argument for copy_tree() like this:
    
    >    if (m->mnt_group_id == last_dest->mnt_group_id) {
    >        type = CL_MAKE_SHARED;
    >    } else {
    >        type = CL_SLAVE;
    >        if (IS_MNT_SHARED(m))
    >           type |= CL_MAKE_SHARED;
    >   }
    
    The "type" argument then governs clone_mnt() behavior with respect to flags
    and mnt_master of new mount. When we iterate through a slave group, it is
    possible that both current "m" and "last_dest" are not shared (although,
    both are slaves, i.e. have non-NULL mnt_master-s). Then the comparison
    above erroneously makes new mount shared and sets its mnt_master to
    last_source->mnt_master. The patch fixes the problem by handling zero
    mnt_group_id-s as though they are unequal.
    
    The similar problem exists in the implementation of "else" clause above
    when we have to ascend upward in the master/slave tree by calling:
    
    >    last_source = last_source->mnt_master;
    >    last_dest = last_source->mnt_parent;
    
    proper number of times. The last step is governed by
    "n->mnt_group_id != last_dest->mnt_group_id" condition that may lie if
    both are zero. The patch fixes this case in the same way as the former one.
    
    [AV: don't open-code an obvious helper...]
    Signed-off-by: default avatarMaxim Patlasov <mpatlasov@virtuozzo.com>
    Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
    f4e8208d
pnode.c 10.2 KB